Response: 

Islam let even a breastfed girl be wed and used as a sex object. This has absolutely nothing to do with the excuse of “reproduction” that Islam apologists like Daniel Haquiqajou make. This Islamic ruling is purely for the benefit and pleasure of old men, while Islam didn't respect the rights of girls. 

'Aisha was wed to Muhammad at the age of 6 years when she was not even able to give her consent. Yes, Abu Bakr didn't have to ask her about her consent, but he directly married her to Muhammad. Later, at the age of 9 years, she was sent to Muhammad's home for the consummation of the marriage. But it is not necessary for Islamic Sharia to wait till the age of 9 years to send the minor girl to her husband's house, but she could be sent to him even if she is a breastfed baby. 

Actually, Muslim men were buying small slave child-girls from the Islamic Bazaars of slavery, and then using them for sexual pleasures. It happened due to another evil of Islamic slavery, where Islam allowed the owners to separate the children from their slave parents, and sell them in the Bazaars of slavery when they got 2 teeth (i.e. at the age of 6 months). 

Moreover, there are authentic reports that companions of Muhammad not only used to rape captive women, but also captive pre-pubescent minor girls. 

Musnad Ahmad, Hadith 22967:

Narrated Buraydah: 
I hated Ali as I had never hated anyone. ... The Prophet sent to us Ali, and among the female captives was a slave girl who was the finest of the female captives, and he apportioned the Khums (one-fifth of war booty given to the Prophet and his family). Ali divided the shares, and his head was dripping (after taking a ritual bath following sexual intercourse with the slave girl). We said: "O Abu al-Hasan (i.e. Ali), what is this?!" Ali replied: "Did you not see the slave girl who was among the female captives? I divided the shares and apportioned Khumus. Then she became part of the Khumus. Then she became part of the household of the Prophet, and then she became part of the house of Ali, and (thus) I had sexual intercourse with her." ...
Grading: Classed Sahih by al-Arna'ut

Since Ali raped that captive girl the same night without any Istibra, thus some people criticized this action of Ali.

Ibn Hajar al-Asqallani answered this criticism, and wrote (link):

وقد استشكل وقوع على على الجارية بغير استبراء وكذلك قسمته لنفسه فأما الأول فمحمول على أنها كانت بكرا غير بالغ ورأى أن مثلها لا يستبرأ كما صار إليه غيره من الصحابة
"It was problematic that Ali Had sexual intercourse with the slave girl without observing Istibra, and also that he apportioned a share for himself. As for the first issue, it is understood that she was a virgin and not pubescent. He recognized that someone like her need not observe Istibra, and it is in accordance with the practice of other Companions."
Ibn Hajar, Fath al-Bari 8/67.

Please read our detailed article: Islam: Even a breastfed baby Girl can be married and used for sexual pleasure

Furthermore, Human nature dictates that as boys and girls reach adulthood, they naturally experience feelings of love. However, Islam denies girls the right to freely fall in love with a boy of their choice. They can be married off to older men, depriving them of the opportunity to develop natural affection for someone their age. If they dare to follow their heart and develop feelings for a boy of their choice, they may face severe consequences such as beatings or even death, all in the name of terms like modesty, decency, adultery, or Ghairah.

Extreme Dangers for teen mothers and their babies

Secondly:

1. Science says 25-30 is the age of least risk to mother and child for a first pregnancy:

https://www.pnas.org/content/113/19/5227 

"With the onset of puberty, the female developmental trajectory diverges substantially from the childhood trajectory, whereas the male trajectory essentially continues its earlier course (Table S2). As a result, the female pelvis attains its obstetrically most favorable morphology around the age of 25–30 y, i.e., at the age of highest fertility"

2.. The younger the mother, the greater the risk. Childbearing in adolescents aged 12–15 years in low resource countries: a neglected issue. New estimates from demographic and household surveys in 42 countries:

https://obgyn.onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0412.2012.01467.x 

"It is frequently cited that girls who give birth aged 15–19 are more than twice as likely to die as those in their 20s (1, 2). However, this fails to capture the fact that risk increases with decreasing age. ......girls aged 15 or under had an odds ratio for maternal death four times higher than women aged 20–24. "

3. It is not just mortality, it's fistulas. Science says it is a problem:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3877393/

"In sub-Saharan Africa and South Asia, obstetric fistula is very common, as access to and use of emergency obstetric care is limited ...... Several factors have been linked to the high occurrence of obstetric fistula in sub-Saharan Africa, including the preponderance of early marriage and teenage pregnancy, which in turn mean that the girls do not have pelvises which have sufficiently developed to allow reproduction [10]. This is further compounded by the poor nutritional status of most of the girls who live in these highly deprived settings [11,12]."

4. Aid workers confirm death and fistulas are the problems:

https://www.livescience.com/19584-10-year-birth.html

"The greatest danger, however, is to the pelvic floor. Girls may start ovulating and menstruating as early as age 9, though the average is around 12 to 13. ........ Just because a girl can get pregnant, though, doesn't mean she can safely deliver a baby. The pelvis does not fully widen until the late teens, meaning that young girls may not be able to push the baby through the birth canal. The results are horrific, said Wall and Thomas, who have both worked in Africa treating women in the aftermath of such labors. Girls may labor for days; many die. Their babies often don't survive labor either.

The women and girls who do survive often develop fistulas, which are holes between the vaginal wall and the rectum or bladder. When the baby's head pushes down and gets stuck, it can cut portions of the mother's soft tissue between its skull and her pelvic bones. As a result, the tissue dies, and a hole forms. Faeces and urine then leak through the hole and out of the vagina. Women with fistulas are often divorced and shunned. And young girls are at higher risk.”

Even if they survive, still the Children of teen mothers suffer dreadful health problems their entire life

High mortality rate among babies from teen mothers is not the only problem, they also suffer from other horrific health problems too their entire life.

https://en.wikipedia.org/wiki/Teenage_pregnancy#Child

• Early motherhood can affect the psychosocial development of the infant. The children of teen mothers are more likely to be born prematurely with a low birth weight, predisposing them to many other lifelong conditions.^[32] 
• Children of teen mothers are at higher risk of intellectual, language, and socio-emotional delays.^[30] 
• Developmental disabilities and behavioral issues are increased in children born to teen mothers.^[33][34] 
• One study suggested that adolescent mothers are less likely to stimulate their infant through affectionate behaviors such as touch, smiling, and verbal communication, or to be sensitive and accepting toward their needs.^[33]
• Poor academic performance in the children of teenage mothers has also been noted, with many of the children being held back a grade level, scoring lower on standardized tests, and/or failing to graduate from secondary school.^[26]  
• Sons born to teenage mothers are three times more likely to serve time in prison.^[37]
  

 

Laws BEFORE Muhammad:

(Credit: Ohana_is_family, who provided the following information)

Many Societies knew the dangers to 9-year-old minor mothers and their babies long BEFORE Muhammad, and they didn't use them for breeding.

(1) The Jews at the time had already set the marriage age to 12:

Pious and Rebellious,Grossman, Avraham;,Brandeis University Press:

Intense opposition to the marriage of young girls is brought in the name of R. Shimon bar Yohai, that “Whoever marries off his daughter when she is young minimizes the bearing of children and loses his money and comes to bloodshed.”5 5. Avot de-Rabbi Nathan, Version II, ch. 48, p. 66. The concern is that the young girl may become pregnant and die as a result.

In fact, Sparta raised the marriage age from 18 to 20 with the primary aim of decreasing the number of sickly children. As a result, they observed an increase in life expectancy for women, which began to rival that of men. It became evident that child marriage was the main contributing factor to mortality rates.

https://en.wikipedia.org/wiki/Women_in_ancient_Sparta#Marriage

• While Athenian women might have expected to marry for the first time around the age of fourteen to men much older than them, Spartan women normally married between the ages of eighteen and twenty to men close to them in age.^[29]
• According to Spartan ideology, the primary role of adult women was to bear and raise healthy children. This focus on childbearing was likely responsible for the emphasis on physical fitness in Spartan women, as it was believed that physically stronger women would have healthier children.[32] 
• Bearing and raising children was considered the most important role for women in Spartan society; equal to male warriors in the Spartan army.^[50] Spartan women were encouraged to produce many children, preferably male, to increase Sparta's military population. They took pride in having borne and raised brave warriors.^[51]

Hence, even with an emphasis on bearing numerous children, Sparta raised the age of marriage for women to 18–20 years. Interestingly, this decision did not hinder Spartan women from having many children. On the contrary, it led to a decrease in the mortality rate among both mothers and children. Additionally, this measure curbed the birth of weak offspring prone to diseases. As a result, only healthy and robust children were born, growing up to become outstanding warriors.

Laws at the time of Muhammed.

The two dominant neighbouring empires had already prohibited intercourse with 9 years old girls before Muhammad.

Laws at the time of Muhammed Minor Marriage in Early Islamic Law, Carolyn G. Baugh, LEIDEN | BOSTON, 2017

"Although investigation into Sasanian-era (224–651 CE) child marriage prac-tices unearths scant information, the age of twelve is again important for girls. According to the Avesta, the age of majority was clearly set at fifteen for boys as well as girls; Middle Persian civil law allowed marriage at age nine, provided that consummation wait until age twelve.[24]"

Byzantine law required that a girl attain the age of thirteen before contract-ing a marriage. Whether she would have consented to the marriage or not prior to this age is deemed immaterial as she would have no legally viable consent to give.[22] All parties to a marriage needed to issue consent, including the groom, the bride, and her parents. In cases where a girl consented to intercourse prior to marriage it was assumed that she consented to the marriage itself and the families would then arrange it. However, if that intercourse occurred prior to the age of thirteen, the groom would meet with the law’s most serious punish-ments due to the girl’s assumed legal inability to consent.[23]"

At the time of Muhammed it was known to be injurious to girls to engage in very early intercourse. 

CHILD MARRlAGE IN ISLAMIC LAW, By Aaju. Ashraf Ali,  THE INSTITUTE OF ISLAMIC STUDIES MCGILL UNIVERSITY, MONTREAL, CANADA, August, 2000  pp 106-107 

Medical Consequences of Child Marriage:

Modem Medicine shows that childbirth for females below the age of seventeen and • above forty leads to greater maternal mortality as well as infant mortality (London  1992, 501). It must he made clear that although conditions commonly associated with poverty, e.g. malnutrition, poor physical health and other negative circumstances may contribute to difficult births and bad health for young mothers, consistent findings indicate that the age factor plays a significant role by itself. "Even under the best of modern conditions, women who give birth before the age of seventeen have a higher mortality rate than older women. The closer a woman is to menarche, the greater the risk to both mother and child, as well as to the mother's future child bearing capabilities, for the reproductive system has not completely matured when ovulation begins". (Demand 1994, 102).

Another problem seen more often among underprivileged women is that they develop **fistulae which is often due to the pelvis not having fully formed. This can be caused by a complicated pregnancy or having intercourse at a very young age.**28. This leads the girl or woman to have permanent damage and often she is shunned by her family and community (4). Although such a condition is preventable it requires a good health service and communications systems (S). Unfortunately, these are often not available in impoverished areas of the developing world.

Knowledge of medical complications involved with early marriage cannot be considered "new" findings. Ancient and Medieval Medicine texts indicate that doctors were well aware of the physical harm posed to girls by early marriages and pregnancies. ……..In fact, not only doctors of Medicine but other scholars in Most societies had a clear understanding that intercourse should not take place before the menarche. Hesiod suggested marriage in the fifth year after puberty, or age nineteen, and Plato in the Laws mandated from sixteen to twenty years of age, and in the Republic he gave the age as twenty. Aristotle specifically warned against early childbearing for women as a cause of small and weak infants and difficult and dangerous labor for the mother, and the Spartans avoided it for just those reasons. (Demand 1994, 102)

Daniel: “Child Sexual Abuse (CSA)” is supposedly accepted and safe

Then Muslim preacher Daniel mentions “evolutionary adaptive”, and claims that academics agree with him that “Child Sexual Abuse (CSA)” is supposedly accepted and safe. And as proof, he put the “Bruce Rind Study”.

But it was again a deception by Daniel on many accounts:

• Rind Study was not about the reproduction of children, which is the main argument by Muslims for early marriages of prepubescent girls in order to defend Islam. 
• Rind Study was only limited to 'long term effects' upon children, who were raped. It concluded that there were no significant long-term effects found in children, who were abused. But this rape was mostly a one-time phenomenon, and not living constantly in such a situation, as it happens in a husband-wife relationship. Those children grew up, found their love and partners, married, and led family life etc.
• This study does not deny the short-term traumas of these children. 
• Whether it is a rape of adult women, or of children, it stays a crime. It does not become permissible while one study didn't find long-term effects due to rape. 

Moreover, it was a complete absence of Academic Integrity from Daniel:

• He does not think his audience deserves to know that his source is highly controversial. The Rind is one of the most controversial papers ever. (Link: https://en.wikipedia.org/wiki/Rind_et_al._controversy)
• He also omits that Rind et al stated that CSA (Child Sexual Abuse) should remain criminalized, which is irreconcilable with Daniel claiming that CSA is supposedly acceptable and safe.
• The Rind et al. study has been criticized by many scientists and researchers, on the grounds that its methodology and conclusions are poorly designed and statistically flawed.^[4][5][6] Its definition of harm, for example, has been the subject of debate, as it only examined self-reported long-term psychological effects in young adults. In contrast, harm can have several forms, including short-term or medical harm (for example, sexually transmitted infections or injuries), a likelihood of revictimization, and the amount of time the victim spent attending therapy for the abuse.^[6] Numerous studies and professional clinical experience in the field of psychology, both before and after Rind et al.'s publications, have long borne out that children cannot consent to sexual activity and that child and adolescent sexual abuse cause harm.^[7][8][9] Psychologist Anna Salter comments that Rind et al.'s results are “truly an outlier” compared to other meta-analyses.^[9]

Daniel also defended that women should not be given Equal Rights, as it will destroy society. Please read our article: Patriarchy: Argument from Muslim Preachers why women should not be given EQUAL Rights and must be kept under men.