Finally, someone has given me what I believe is a good argument against homosexuality, other than just quoting scripture. I hate when as Christians we only make arguments to non Christians as to what our Scripture says.
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 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.