Because the pig can't really consent, now can it? I suppose it could wiggle its rump suggestively or something, but given the total, ah, language barrier, Billy-Bob would be hard put to say his prize sow was gagging for it, and this could get absolutely repulsive if I continued in this vein so never mind.
I don't think the Bible calls for stoning homosexuals, just those who practice sodomy (or, for that matter, get blowjobs, or beat off, or anything- it's all kinda lumped together). I won't bother with this whole "straight people butt**** too" crap, because once again it's not a category of things you can do with your dick that I particuarly want to know about. BUT, there's no distinction between gay intercourse and what pretty much every person has done by age 15, so either everyone's going to hell (which, given the rules, can't be such a bad place after all), or the Bible was made as a code of law primarily reflecting the sensibilities of the time, which has damn little to do with what any God had to say in the matter, or (particularly) has to say now.
'Sides, I think the current right-wing argument is more along the lines of "Oh, now they're gonna legalize prostitution, too, right?"
Which, honestly, I don't see the problem with, so long as it's properly regulated, but hey. Whatever floats their freaky, angry boats.