From the catechism here is the first part of the definition of sin:
“Sin is an offense against reason, truth, and right conscience”
and from the definition the of mortal sin:
Mortal sin requires full knowledge and complete consent.
Therefore, the Catechism clearly establishes that in order for a person to commit a sin the act must be at conflict with their conscience and for that to happen they must be aware it is wrong on at least some level.
However, what the world would have us believe is that people are born **biologically **to commit certain actions/sin. Nonetheless, given that God is the author and designer of all biological systems this creates a polemic and allows only two possible interpretations:
You are incorrect, and your logic is faulty.
From the CCC (underline mine):
*FREEDOM AND RESPONSIBILITY
1731 Freedom is the power, rooted in reason and will, to act or not to act, to do this or that, and so to perform deliberate actions on one’s own responsibility. By free will one shapes one’s own life. Human freedom is a force for growth and maturity in truth and goodness; it attains its perfection when directed toward God, our beatitude.
1732 As long as freedom has not bound itself definitively to its ultimate good which is God, there is the possibility of choosing between good and evil, and thus of growing in perfection or of failing and sinning. This freedom characterizes properly human acts. It is the basis of praise or blame, merit or reproach.
1733 The more one does what is good, the freer one becomes. There is no true freedom except in the service of what is good and just. The choice to disobey and do evil is an abuse of freedom and leads to "the slavery of sin."28
1734 Freedom makes man responsible for his acts to the extent that they are voluntary. Progress in virtue, knowledge of the good, and ascesis enhance the mastery of the will over its acts.
1735 Imputability and responsibility for an action can be diminished or even nullified by ignorance, inadvertence, duress, fear, habit, inordinate attachments, and other psychological or social factors.
1736 Every act directly willed is imputable to its author:
Thus the Lord asked Eve after the sin in the garden: "What is this that you have done?"29 He asked Cain the same question.30 The prophet Nathan questioned David in the same way after he committed adultery with the wife of Uriah and had him murdered.31
An action can be indirectly voluntary when it results from negligence regarding something one should have known or done: for example, an accident arising from ignorance of traffic laws.
1737 An effect can be tolerated without being willed by its agent; for instance, a mother’s exhaustion from tending her sick child. A bad effect is not imputable if it was not willed either as an end or as a means of an action, e.g., a death a person incurs in aiding someone in danger. For a bad effect to be imputable it must be foreseeable and the agent must have the possibility of avoiding it, as in the case of manslaughter caused by a drunken driver.
1738 Freedom is exercised in relationships between human beings. Every human person, created in the image of God, has the natural right to be recognized as a free and responsible being. All owe to each other this duty of respect. The right to the exercise of freedom, especially in moral and religious matters, is an inalienable requirement of the dignity of the human person. This right must be recognized and protected by civil authority within the limits of the common good and public order.32
II. HUMAN FREEDOM IN THE ECONOMY OF SALVATION
**1739 Freedom and sin. *
Man’s freedom is limited and fallible. In fact, man failed. He freely sinned. By refusing God’s plan of love, he deceived himself and became a slave to sin. This first alienation engendered a multitude of others. From its outset, human history attests the wretchedness and oppression born of the human heart in consequence of the abuse of freedom.
You are on top of that accusing me of saying things I did not say. I did not say that people were born to commit certain offenses. I said that a) we are born in original sin, which is none of God’s doing but still puts us in a state of concupiscence and b) that the Church acknowledges that some people are constitutionally attracted to persons of their own sex, even though acting on that attraction would be gravely immoral. Finally, and yet again: The OP said very clearly that the young man in question is neither violating chastity nor advocating for anything like what you are implying he is. Really, you have been very rash about your judgments of him.
The Church does not teach that our free will operates without any fetters. The Church is willing to concede that a biological basis may be responsible for some psychological orientation towards homosexual acts. That is a million miles from saying that committing the act isn’t a sin–and more to the point, this friend of the OP’s daughter has not done a thing to imply that he thinks so!