Many who claim that homosexuality is morally benign claim that same-sex attraction is “in their genes.”  Does this appeal to biological determinism help their case?  No.  No moral truth follows from biological truth.  Even if it were true that same-sex attraction was biologically determined (something for which there is no solid evidence), it would no more follow that homosexuality is, therefore, morally benign, than it would follow that pedophilia is morally benign if a genetic link to pedophilia was discovered.

Furthermore, if biologically predisposed/determined behaviors are excused from moral condemnation, then on what basis could bigotry against homosexuals be condemned if the desire to discriminate against homosexuals is caused by one’s genes?  If hatred of homosexuality is biologically determined, and thus it is morally benign.  After all, such a person would be born that way!  Surely no one would buy this argument, and yet it is logically equivalent to the argument that homosexuality is morally benign because it is biologically determined.  If we have reason to reject one form of the argument, we have reason to reject the other.  The fact of the matter is that biology tells us nothing about morality.