Many homosexuals argue that they have not chosen their condition, but that they were born that way, making homosexual behavior natural for them.
But because something was not chosen does not mean it was inborn. Some desires are acquired or strengthened by habituation and conditioning instead of by conscious choice. For example, no one chooses to be an alcoholic, but one can become habituated to alcohol. Just as one can acquire alcoholic desires (by repeatedly becoming intoxicated) without consciously choosing them, so one may acquire homosexual desires (by engaging in homosexual fantasies or behavior) without consciously choosing them.
Since sexual desire is subject to a high degree of cognitive conditioning in humans (there is no biological reason why we find certain scents, forms of dress, or forms of underwear sexually stimulating), it would be most unusual if homosexual desires were not subject to a similar degree of cognitive conditioning.
Even if there is a genetic predisposition toward homosexuality (and studies on this point are inconclusive), the behavior remains unnatural because homosexuality is still not part of the natural design of humanity. It does not make homosexual behavior acceptable; other behaviors are not rendered acceptable simply because there may be a genetic predisposition toward them.For example, scientific studies suggest some people are born with a hereditary disposition to alcoholism, but no one would argue someone ought to fulfill these inborn urges by becoming an alcoholic. Alcoholism is not an acceptable "lifestyle" any more than homosexuality is.
From the Holy Bible, the Word of God:
Leviticus 20:13: If a man lies with a male as with a woman, both of them have committed an abomination; they shall be put to death, their blood is upon them.
Romans 1:26-28: For this reason God gave them up to dishonorable passions. Their women exchanged natural relations for unnatural, and the men likewise gave up natural relations with women and were consumed with passion for one another, men committing shameless acts with men and receiving in their own persons the due penalty for their error. And since they did not see fit to acknowledge God, God gave them up to a base mind and to improper conduct.
1 Timothy 8-11: Now we know that the law is good, if any one uses it lawfully, understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for murderers of fathers and murderers of mothers, for manslayers, immoral persons, sodomites, kidnapers, liars, perjurers, and whatever else is contrary to sound doctrine, in accordance with the glorious gospel of the blessed God with which I have been entrusted.