If I still had my facebook and I saw that s**t pop up, I'd verbally b***h-slap that ********.
I have friends that don't particularly like the fact that some people are gay, and even the most religious of them manage to not post anything like that on their walls (or whatever they're called) because they have enough respect for individuals to keep potentially harmful opinions to themselves.
The only issue that I'm torn between is the ones who would oppose it should it be put up to vote - but I'm not really sure if they'd actually vote in that at all were it to come up.
The one guy votes republican, but he'd vote republican regardless of whether or not they were for gay marriage anyway, just like my one other friend who votes democrat despite not particularly liking the idea of gay marriage.
I've also had discussions with people about this kind of stuff in the past and should they pull out a religious reasoning, I simply tell them that I am not religious and their religious edicts should not apply to me in a nation that enables religious freedom. Everyone who I've discussed this with has ended up agreeing that their religiously-oriented views shouldn't be forced on me, an atheist.