Firstly: Islam usurps the right from a small girl to indulge in love, by forced marriage without her consent

Islam allows the father/guardian to forcefully give a minor girl in Nikah of any man, even if he is 50 years old. The father/guardian does not even need to ask for the consent of a minor girl.

Abu Bakr gave 6 years old small child 'Aisha in marriage of the old person like Muhammad without even asking it from 'Aisha. 

Therefore, the most important question is what chance does such a minor child girl have, to become an adult, and to fall in natural love with any boy of her own age group? 

And the answer is, she has absolutely no chance. 

Islam usurped her right of felling in love completely. And now Islam is forcing her to love only that old man to whom she was married by her guardian without her consent. 

It is a wonder that despite this oppression, still Muslim claim Islam to be a religion of nature. 

Secondly: 

Islam Preachers claim that Muhammad wed young 'Aisha, while she was able to absorb a lot of knowledge due to her young age. 

Answer:

Absorbing knowledge is not conditioned to young age, but it is conditioned to INTELLIGENCE and memory.

Abu Hurayrah accepted Islam at the age of 26, and he stayed with Muhammad for only 3 years. Yet, he absorbed much more knowledge from Muhammad. He narrated 5,374 hadiths from Muhammad, while 'Aisha absorbed less knowledge despite younger age, and she narrated only 2,210 hadiths from Muhammad.

Muhammad also had wives like Saffiya and others who were 15 to 20 years of age. An intelligent 16 years woman is in much better position in order to understand the issues, and to absorb knowledge and preserve it, as compared to a 9 years old, who used to play with dolls (Sahih al-Bukhari, 6130) even after she entered the house of Muhammad at the age of 9 years. 

Sahih Bukhari, 6130:

Narrated `Aisha: I used to play with the dolls in the presence of the Prophet (i.e. after the marriage was consummated at the age of 9 years), and my girl friends also used to play with me. When Allah's Messenger (ﷺ) used to enter (my dwelling place) they used to hide themselves, but the Prophet would call them to join and play with me. (The playing with the dolls and similar images is forbidden, but it was allowed for `Aisha at that time, as she was a little girl, not yet reached the age of puberty.) (Fath-ul-Bari page 143, Vol.13)

Thirdly:

Islam Preachers also come up with an excuse that Muhammad wed young 'Aisha, so that she could live long enough after the death of Muhammad to spread his teachings. 

Answer: 

And if there really exists any Allah, and HE also wished to prolong the life of any wife of Muhammad, then a 16 years old woman can also last longer enough to spread the knowledge.

'Aisha died at the age of 65 years. So, was it difficult for Allah to prolong the life of any other adult wife of Muhammad to 70 years or 80 years?

Fourthly:

Islam Preachers claim that 'Aisha was fully satisfied and happy with that marriage later, and she didn't complain about it. 

Answer:

Sometimes oppression goes to that extent, where human beings forget about their basic human rights, and they start considering that oppression to be the right thing. 

The same logic was used by the slave owners when Abraham Lincoln abolished slavery. Many slaves returned to their owners, while they were so much brainwashed that they didn't want to have their freedom, but they were satisfied for being a slave and deprived of all human rights as free men. 

These evil customs and practices of societies stay wrong, even if they succeed in brainwashing oppressed people in believing in those evils to be their fate. 

Fifthly:

Next problem is this that marriage with non-adult girls is not limited only to 'Aisha, but it is a GENERAL Ruling that it is Halal for any father/guardian to wed her non-adult daughter with any man of his own choice, without her consent.

These other non-adult girls don't have to absorb any knowledge to give it further (like in case of 'Aisha). So, why then Islam oppressed them in this way?

Islam allows all men to marry minor girls and to undress them, and to kiss their naked bodies, and to rub their penises in their thighs to ejaculate, and to take all other kinds of sexual pleasures from them (except penetration into their vaginas), even though those minor girls don't need to absorb any knowledge like 'Aisha. 

Please read our detailed article:

Islam: Even a breastfed baby Girl can be married and used for sexual pleasure

Sixthly:

Islam preachers also come up with an excuse that it was tradition of that era that minor girls were also married without their consent, so we should not question this Islamic Ruling today.

Answer:

Off course, this wrong Islamic Ruling is questioned in all accounts. 

Firstly, even if we assume it was a practice of that era, still the question is why didn't Allah/Muhammad abolished this wrong practice and put a ban upon it? What to talk about banning it, Muhammad didn't even condemned this practice orally. Actually, contrary to it, he himself encouraged people to involve in this evil practice by making it a Sunnah by marrying 'Aisha. 

Secondly, Islam preachers are telling a lie that it was a practice of that era. 

The Romans were well aware that pregnancies in young women were very dangerous because the pelvic floor and birth-canal do not widen until the late teens.

The Roman doctor Soranus wrote in his book about gynecology in the section about problematic deliveries: (link): 

"For it obtains whenever women married before maturity conceive and give birth while the uterus has not yet fully grown nor the fundus of (the) uterus expanded*."* So they knew the pelvic floor and birth canal were not mature enough.
Moreover, he also wrote (link):
"..difficult labor occur in those who give birth in a way which is contrary to nature? Diocles the Caerystan in the second book on gynecology says that primiparae and young women have difficult labor"
Moreover, he also wrote (link):
"How to Recognize Those Capable of Conception: Since women usually are married for the sake of children and succession and not for mere enjoyment and since it is utterly absurd to make inquiries about the excellence of their lineage and the abundance of their means but to leave unexamined whether they can conceive or not and whether they are fit for childbearing or not it is only right for us to give an account of the matter in question One must judge the majority from the ages of 15 to 40 to be fit for conception"

Soranus made these suggestions against marrying under 15, about 500 years before Muhammed had intercourse with 9 year old Aisha.

Under the suggestions of Soranus, the two empires of that time prohibited intercourse with 9 years old girls. 

​ Book: Laws at the time of Muhammed Minor Marriage in Early Islamic Law, Carolyn G. Baugh, LEIDEN | BOSTON, 2017 (link):

"Middle Persian civil law allowed marriage at age nine, provided that consummation wait until age twelve"

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. 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."

So the 2 dominant neighbouring empires prohibited intercourse with 9 year olds .

In Roman Egypt, Basra etc. a man could get severe punishments for seducing a girl under 13 because she was too young to give consent and not capable of fully understanding the risks to her.

Medically speaking it was known to be dangerous and had been so for centuries. At the time of Muhammed it was known to be injurious to girls to engage in very early intercourse.

Reference: CHILD MARRlAGE IN ISLAMIC LAW, By Aaju. Ashraf Ali, 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. This leads the girl or woman to have permanent damage and often she is shunned by her family and community.
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)
Nevertheless, Greek culture in general, like so Many others, disregarded such realities and continued to favour early childbearing (102). Rabbis too were aware that pregnancy in such young females was undesirable because the birth could result in the mother's death. "They could not, however, outrightly prohibit such maniages, which were common practice in the Orient . . . therefore [they] recommended the use of a contraceptive" (Preuss 1978, 381).
So intercourse with 9 year olds was not "accepted" or "the norm" it was known to be dangerous. Mortality, infertility and traumatic fistula were known risks of early intercouse and Mortality, obstetric fistula etc. were known risks of early pregnancies.

Muhammed's behaviour to a 9 year old was immoral because she was at serious risk of harm while being too young to understand the risks to her.

Seventhly:

A new group among Muslims have emerged in this century, which claims that 'Aisha was not 9 years old, but 19 years old at the time of consummation of marriage. 

Answer:

This group presents only ONE reference for their claim. 

While on the other hand, we have 18 Sahaba and Tabaeen who recorded that 'Aisha was 9 years old at the time of consummation of marriage. The name of these 18 Sahaba and Tabaeen are as under:

  1. 'Urwa bin Zubair (Sahih Bukhari, Sahih Muslim)
  2. Aswad bn Yazid (Sahih Muslim)
  3. Abdullah Ibn Saffwan (Mustadrak al-Hakim)
  4. Abdullah ibn Abi Mulaikah (Sunan Nisai)
  5. Abu Salama bn Abdul Rehman (Sunan Nisai)
  6. Qasim bin Muhammad (Tibrani)
  7. Abdul Malik bin 'Umair (Tibrani)
  8. Abdul Rehman bin Muhammad bin Zayd (Tibrani)
  9. Yahya bin Abdul Rehman bin Hatib (Musnad Ahmed bin Hanbal)
  10. 'Umra bint Abdul Rehman (Ibn Saad)
  11. Abu 'Ubaida (Sunan Nisai)
    And then there are other Sahaba (companions) and Tabaeen too who testified of her age to be 9 at time of marriage (but they didn't narrate it directly from 'Aisha). For example:
  12. Abu 'Ubaida from Abdullah Ibn Masood (Sunan Ibn Majah)
  13. Abu Ishaaq from Mua'sab bin Saad (al-Tabqaat)
  14. Yazid bin Jabir from his father (al-Mustadrak)
  15. Abu 'Ubaidah from Jabir bin Zayd (Musnad al-Rabi'i)
  16. Habib, the slave of 'Urwa (Mustadrak al-Hakim)
  17. Jaffar bin Burqan from Zuhri (al-Tabaqaat)
  18. Saeed bin Abi 'Aroba from Qatada (Tabrani) 

This is an absolute double standard by these few modern Muslims to reject all these Ahadith from 18 Sahaba and Tabaeen (including 'Aisha herself), and go for a vague one tradition.

You can read more about this one vague tradition here.

https://wikiislam.net/wiki/Aisha%27s_Age

Eighthly:

Pakistani Muslim Scholar Ghamidi also denies the age of 'Aisha to be 9 at time of consummation of marriage. His argument is this that the prophet wanted to have a grown-up mature wife to look after his house affairs and his little daughters. Therefore, at age of Nikah, 'Aisha's age was 16 years, and at time of consummation of marriage, she was 19 years old.

This is a lame excuse by Ghamidi, while if we accept that age of 'Aisha to be 16 at the time of Nikah, then a 16 years old girl could easily look after the children and household. Why then did the prophet have to wait 3 more years (till she became 19) to bring her to his home? If he really needed a woman for household, then he should have immediately brought her to his home and consummated the marriage. Why then wait 3 more years?

And the prophet did Nikah with 'Aisha even before Sawdah. And if 'Aisha was really 16 years old, then he didn't need to marry an old woman Sawdah any more while 16 years old 'Aisha would have been enough to look after his daughters and the household.