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Like it or not, think it's pejorative or not, the current logic people are using to justify and legalize gay relationships applies equally to other non-abusive relationships, including polygamy, polyamory and bestiality.  Are we saying that homosexuality and beastiality are the same, morally speaking?  No, but I'm not sure why bestialists are judged as 'bad' – I mean, it may seem 'gross' to us, but who are we to judge?  You can't have it both ways if you want to be logical.

And The People's Cube has a really witty article on this – but if you can't take the humor, and are deeply offended, your misplaced sense of self-righteousness will certainly keep you from seeing the point.  Here's the intro:

This tax season you have surely wondered why you weren't allowed to claim your talking parakeet as a dependent. Many of you maintain a strong loving relationship with your cats, dogs, hamsters, or sheep. You can't imagine life without your pet – just like your next door neighbor whose companion happens to be human – yet you are denied the same rights, respect, and recognition that your neighbor enjoys – only because your companion happens to be a member of another species.