Alright, so if you're willing to grant that abnormal isn't always a problem, then you then have to establish that homosexuality is abnormal in such a way as to be a problem. If homosexuality is not 'a problem', the rest of your argument can't go forward. So why is homosexuality a problem? I'm pretty sure this brings us back to biological imperative, which I addressed a bit in my previous post. So a same-sex couple can't produce children. Less say your significant other is sterile, is it immoral to be allowed to marry them over someone who can produce children?