You are obviously ignorant of anatomy and physiology.
The sun is particularly well suited to warm the earth.... but is that its purpose?
Oh I know the basics of anatomy and physiology, and a little bit beyond. But "purpose" and "function" (ie, a task to which something is particularly well suited) are getting confused here. Purpose implies intent, while function does not, necessarily. So maybe you want to say that our DNA, our hands, our reproductive organs were designed with intent, and purpose, and that to violate the goals of that design is some sort of moral wrong. But at that point one is speaking theology, and is most definitely not speaking scientifically, or medically - as so often these arguments about "abnormality" or "aberrations", etc are dressed.
But maybe our body parts just have some functions, even if they don't have a purpose or if that purpose is hidden or controversial. Perhaps you also want to say its an aberration to use our body parts for functions or tasks to which they are not particularly well suited - or perhaps its an aberration when we don't use them in a capacity that utilizes all their features... but again, who cares? There's no moral component there... or if there is, a better case needs to be made for it, and as of yet, none has.
You unilaterally declaring something a human right does not make it so. Again, please demonstrate the moral imperative.
Are you on record endorsing unqualified egalitarianism or are there limits to what a society should accept?
It seems to me if you claim the former you admit some rather noxious behaviors far and above mere homosexuality. If you claim the latter than you admit there are limits and maybe your claims aren't as sacrosanct after all.
I think perhaps the best way to safeguard rights, is to make sure they are applied to everybody, and can only be restricted for non-arbitrary and justifiable reasons. If you want to call marriage a "privilege"** - fine, but the same thing applies to those too. So far, "arbitrary" seems like the absolute perfect word to describe every single argument against same-sex marriage I have ever seen.
** Though I generally think of privileges as things that can be revoked or given, arbitrarily, e.g. Its a privilege to
borrow my car, but not a privilege to have a drivers license - that's a right. Maybe its a privilege to win consent from the person you love for their hand in marriage - but its a right to actually
get legally married.