Islamic Hijab and Islamic Modesty are against Nature. This is proven from the CONTRADICTIONS that occur in Islam due to these unnatural rulings. 

Islam does not even allow the adopted son to see his mother (who raised him as her own son since childhood) after he has become an adult. If they become alone in the house, then it becomes a crime according to Sharia rules and they must be punished for it, while Prophet of Islam said: “No man is alone with a woman except the third one present is the Shaytaan.” Narrated by at-Tirmidhi (2165); classed as saheeh by al-Albaani.

On the other hand, if a man buys a male slave, then he immediately becomes Mahram for the owner's wife, and could enter the house and wife does not need to do Hijab from him, and they could stay under one roof alone too. 

Islam thinks that adopted son (who was raised from the mother right from his childhood and loved from her as her own child) will get lust for his mother, but a male slave will not get lust for his owner's wife and his daughters at home.

Male slave becomes Mahram as soon as he is bought from the market

According to Islamic Sharia, a male slave becomes Mahram to the owner's wife (and daughters too in the house) as soon as he is bought from the market. He could stay alone with her in the house under one roof and she does not need to do Hijab from him and hide her Zinah (i.e. adornment) from him. 

Surah Nur, Verse 24:31:

And say to the believing women (that) they should lower [of] their gaze and they should guard their chastity, and not (to) display their adornment except what is apparent of it. And let them draw their head covers over their bosoms, and not (to) display their adornment except to their husbands, or their fathers or fathers (of) their husbands or their sons or sons (of) their husbands or their brothers or sons (of) their brothers or sons (of) their sisters, or their women or what possess their right hands (i.e. slaves) or the attendants having no physical desire among [the] men or [the] children who (are) not aware of private aspects (of) the women. And not let them stamp their feet to make known what they conceal of their adornment. And turn to Allah altogether O believers! So that you may succeed. (Corpus Quran)

Surah Nur, Verse 24:58:

O you who believe! Let ask your permission those whom possess your right hands (i.e. slaves) and those who (have) not reached puberty among you (at) three times, before (the) prayer (of) dawn, and when you put aside your garments at noon and after (the) prayer (of) night. (Corpus Quran)

And also read the following hadith, where Muhammad was telling his daughter Fatima that she didn't need to do Hijab from the male slave.

Sunnan Abu Dawud, Hadith 4106

The Prophet (ﷺ) brought Fatimah a slave which he donated to her. Fatimah wore a garment which, when she covered her head, did not reach her feet, and when she covered her feet by it, that garment did not reach her head. When the Prophet (ﷺ) saw her struggle, he said: There is no harm to you: Here is only your father and slave.
Grade: Sahih (Albani)

Fatwas that an adopted son becomes Na-Mahram upon puberty and should be separated from his mother who raised him

Fatwa from Sunni website Islamweb.net:

Question from a mother: Is it a sin if I don't observe hijaab in front of my adopted son? I don't want to as it makes him feel like a stranger, and hurts him.Is there any way I can avoid hijab in front of him.

Answer: This boy is considered as a non-Mahram to you. Therefore, if he has reached the age of puberty or nearly so, then you must observe Hijaab in front of him (even if it hurts him), and you are not permitted to be in seclusion with him.

Fatwa from Saudi Salafi Fatwa website: Isalm Q&A:

Question: I am fifteen years old. I was adopted by an Afghan family when I was six months old ... What are the rulings in my situation?

Answer: ...  The woman who adopted you is a non-mahram to you, and it is not permissible for you to see her, let alone touch her or kiss her when you are not a mahram to her or to her daughters. 

If you want to see more cruelty of this Islamic ruling, then look at this fatwa (link), where a Muslim mother was crying and she refused to be separated from her adopted son (while he became an adult at age of 12-13 years).

But the relatives wanted to forcefully separate them (i.e. the mother and the adopted child) from each other, and the Muslim Mufti supported the action of the relatives while it is indeed the order of Allah in Islam, as Allah fears that it will cause the Fitna of fornication if both Na-Mahrams (i.e. mother and her 12-14 years old adopted son) stay together under one roof.

 Are Muslims able to see the calamity that Islam brought upon that poor mother and her child? 

The status of one who fosters and raises a child is HIGHER than the one who gives birth to that child

A child doesn't care who gave birth to him, but he will open his hands and go in the lap of that person who fosters him, who loves him and who takes care of him. 

Even one could see the importance of foster bond in the animal world too. If you keep eggs of hen under a duck, still the chicks of hen will consider that duck their mother as they will see that duck taking care of them. Thus, they will still develop a mother-child bond despite not being related to each other by blood. 

Even if a cat takes care of chicks, then chicks will take that cat to be their mother. 

Indeed, the status of one who fosters and raises a child is higher than the one who gives birth to that child. 

Foster parents-child bond despite having no blood relationship

Remember, when a foster mother or foster father takes care of a child und raises him with love, then the natural parent-child bond automatically develops between them. 

In the history of the whole world, each and every nation accepted this bond between the adopted child and the foster parents. 

All psychiatrists of the world unanimously accept this bond in light of their millions of experiments. 

But Islam is the only one, who denies this natural bond between the foster parents and the child. 

Islam denied this bond only in order to fulfill the lust of one person

Even Islam initially accepted this bond, as it is a Universal Truth. Nevertheless, later happened one incident, and then Islam started denying the presence of any such bond. 

Guess it yourself, why Islam later denied it. 

For further details, and in order to find out the answer (if you don't know it), please read our article: Muhammad's journey from 4 marriages to 9 marriages with the help of Revelations 

Islamic Logic: A woman can develop a mother-son bond with even a grown-up male by breastfeeding him

Sahih Muslim, Hadith 1453a:

Sahla bint Suhail came to Allah's Apostle (may peace be upon him) and said: Messenger of Allah, I see on the face of Abu Hudhaifa (signs of disgust) on entering of Salim (who is an ally) into (our house), whereupon Allah's Apostle (ﷺ) said: Suckle him. She said: How can I suckle him as he is a grown-up man? Allah's Messenger (ﷺ) smiled and said: I already know that he is a young man 'Amr has made this addition in his narration that he participated in the Battle of Badr and in the narration of Ibn 'Umar (the words are): Allah's Messenger laughed.

Human rationale will guide you clearly in this matter that Muhammad's ruling is ridiculous and false, while:

  • If a woman breastfeeds a grown-up male man with mustache and beard, then mother-son bond will not develop, but only the bond of LUST and SEX can develop. 
  • Of course, there can exist a relationship of respect between a woman and a grown-up man, but for that purpose breastfeeding the grown-up male will be the worst possible method. 

For example, if a wife of elder brother behaves like a sister/mother with the younger brother of her husband, and takes care of him, then a relationship of respect will automatically develop between them according to human nature. There are millions (actually billions) of Muslim families who are living in a joint family system in India/Pakistan/Bangladesh, and there is a relationship of respect between a man and wife of his elder brother. This proves that Islam is totally false on this point. 

Even if a mother breastfeeds a small child (under 2 years) for only 5 times (as Islam suggests), still hardly any mother-child bond will develop between them. If child forgets this action of woman due to his small age, then surely there will never develop any such mother-child bond. 

PS:

Islam apologists claim that Muhammad didn't ask Sahla to breastfeed that gorwn-up man, but she pumped her milk into a cup and then gave it to him. 

Nevertheless, this cup claim of Muslims is ridiculous. If it was really a cup thing, then Muhammad would have not laughed upon it, and Sahla would have not shown hesitation in suckling him. Muhammad's laugh makes it clear that it was about suckling directly from the breasts of woman. 

An excuse from an Islam apologist: Male slave became Mahram while situation NEEDED it

An Islam apologist wrote:

If women in house are asked to do Hijab from the male slave, and if he is not considered a Mahram to the wife and daughters of his owner, then it will become impossible to take his services at home. Therefore, a male slave is declared as Mahram in Islam so that he could freely work inside the house. But no such need exists for an adopted son, as he is not needed to work at home.

Answer:

The word "Need" is only a deception here. Actually, it was the Contradictions in Sharia which compelled it to declare a male slave Mahram to all women in the house as soon as he was purchased. 

Why Muslims cannot understand this simple fact that this whole issue of Hijab is Un-Natural. This Hijab had been introduced (prior to Islam) in ancient Mesopotamia and in the Byzantine, Greek, and Persian empires in order to show the higher status of free women as compared to the slave women (link). And Muhammad copied this practice from these old civilizations. 

If the question was only about the "Need", then does Allah thinks a woman loses the Need of her desire to have a child upon his becoming an adult, after raising and loving him for the whole of his life? Or does Allah think that the child does not Need the love and care of his foster mother after becoming an adult? Actually, the poor child is not only losing his mother, but his whole family including his foster father and foster sisters/brothers. If Allah really thinks so, then He is ignorant and He has no idea about human nature. If Allah thinks that a son gets lust of sex with his foster mother as soon as he becomes adult, and the whole mother-child bond disappears, while a male slave immediately became a guard of all women in house without any lust, then one can only beat his chest in grief upon the wisdom of so-called Allah. 

Part 2: Adopted daughter is in danger of being forcefully married by her foster Muslim father if he gets lust for her

For the personal lust for his daughter-in-law (wife of his adopted son), Muhammad first destroyed the sacred bond between the adopted child and the parents. 

And then this Islamic cruelty went further, and it made it Halal for the Muslim foster father to forcefully marry his minor adopted daughter to himself if he got lust for her due to her beauty:

Quran 4:3:
And if you fear that you will not deal justly with the orphan girls, then marry those that please you of [other] women, two or three or four ...

Why Muhammad was forced to claim the revelation of this verse? The following tradition of ‘Aisha makes it clear:

Sahih Bukhari, Hadith 5064:
('Urwa narrated from ‘Aisha that she said about this verse 4:3) "O my nephew! (This Verse has been revealed in connection with) an orphan girl under the guardianship of her guardian who is attracted by her wealth and beauty and intends to marry her with a Mahr (i.e. money for dowry) less than what other women of her standard deserve. So they (such guardians) have been forbidden to marry them unless they do justice to them and give them their full Mahr (i.e. Dowry).

In Islam, a foster father (or guardian) is not needed to ask for the consent from the minor girl child before giving her into Nikah of any man including himself(Link). 

Islam actually took away the right of having father and brother from poor orphan girls. Once she becomes an adult, then not only does she have to observe Hijab from her foster father and foster brothers, but they could also not stay alone under one roof. 

In simple words, the combination of Islamic Hijab + Islamic Modesty + allowing foster father to forcefully marry his adopted daughter even without her consent, this takes away the right of family life from the poor orphan girls.