The following is a paragraph from the blog "Stand to Reason". The blog shows how the argument for homosexuality that is based on inborn biological traits is not only false, but even if it were true would not necessarily defend homosexuality as 'moral'.
A second problem with the born-that-way theory is that even if true, it wouldn’t prove that homosexual behavior is moral. Consider that scientific research has discovered genes they believe contribute to alcoholism, unfaithfulness, violence, and even many diseases. Are we to believe that because there is a genetic contribution to these behaviors (or even if they were genetically determined) that they should be regarded as morally appropriate? Of course not. So, proving homosexual behavior is appropriate by appealing to a genetic determinant is equally spurious.
The whole article is worth reading so do yourself a favor and read it here.