We would like to know the reasons behind forbidding marrying one’s maternal aunt from the psychological, ethical, and social points of view. I already know that there are decisive Islamic texts forbidding it.

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

It is impermissible for a Muslim man to marry his maternal aunt, and this is an established ruling of the Sharee‘ah (Islamic law) supported by the Quran and the Sunnah (Prophetic tradition) and the consensus of Muslim scholars; Allaah the Almighty Says (what means): {“Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters …”} [Quran, 4:23]

There are no differences of opinion among Muslim scholars regarding this prohibition, and it is a rule upon which all Math-habs (schools of thought) agree. No one would approve of such a revolting act except those who go against their sound natural instinct such as the Magians who permitted sibling marriages and marrying one’s Mahram (non-marriageable) female relatives. Indeed, a Muslim fully believes that Allaah The Exalted is All-Wise and All-Knowing; He will not set an obligation unless there is great wisdom behind it whether we knew of it or not.

The well-versed scholar Al-Kaasaani said,

Indeed, marrying one’s female Mahram relatives would eventually lead to severing kinship ties; for marriage cannot be free of potential problems that might arise between the spouses and this would result in some sort of rankle between them which might eventually lead to severing their kinship ties. Therefore, marriage in this case would be a means of severing kinship ties. It is known that anything that leads to what is forbidden is also forbidden. In fact, this applies to all the seven types of Mahram women that were clarified in the verse, for maintaining kinship ties with them is obligatory and unlawful to sever.

Moreover, Imaam As-Sayyid Saabiq elaborated in his book Fiqh As-Sunnah,

The paternal and maternal aunts are like the parents. The Prophet, sallallaahu ‘alayhi wa sallam, said: "The paternal uncle comes from the same root as the father (is like the father)." [Muslim]   The Hadeeth (narration) compares the father and uncle to two plants growing from the same root. Also, the maternal aunt has the same degree of [closeness to] the mother.  Muslim scholars group the prohibition of nephew-maternal aunt marriage with the prohibition of son-mother marriage. Thus, one of the great virtues of Islam is that it complies with sound human nature. Islam maintains the affection between Muslims and their paternal uncles and maternal aunts preserving the necessary compassion and cooperation and shielding these kinship ties against the peril of lust. Thus, Allaah The Almighty prohibits Muslims from marrying their maternal aunts and paternal uncles [niece-uncle and nephew-aunt marriages].

Furthermore, the Prophet, sallallaahu ‘alayhi wa sallam, said: “The (maternal) aunt is of the same rank as one’s mother." [Al-Bukhari] If the maternal aunt has the rank of the mother, then it is obligatory on the son to honor, respect and treasure her. Whereas, had it been allowable for a man to marry his maternal aunt, she would have been obliged to obey him and be at his service which would contradict the apt reverence that is due to the mother’s high status in Islam.

Moreover, how could one even think of marrying his own mother! Obviously, sound human nature abhors marrying one’s Mahram women. On the other hand, corrupted human nature might permit sister-brother, nephew-aunt or niece-uncle marriages. We seek refuge in Allaah The Almighty from such evil.

Were a person to do such an abhorrent act or a nation to permit it, Allaah The Almighty would afflict upon them illnesses, pain, humiliation, shame, destruction,  corruption of their children and families, and severing of their kinship ties. However, these punishments are in this world, whereas the torment that awaits them in the Hereafter would be more painful and more severe.

Allaah Knows best.