Actually, Antechrist is raising some good points about the decisions we make. Is the view against bestiality and zoophilia due to it being harmful to the animal 100% of the time? A lot of the potential actions involved in it aren't harmful to the animal at all, and some cases (like going all Catherine the Great) are more harmful to the human. Some things in bestiality are almost identical to what is done to gather sperm from the animals for scientific reasons, with the intent being what makes it different. In which case, you have to admit that you're only wanting to make it illegal because you basically find it creepy. And you can't really say that the animals suffer psychological scarring; their brains operate on an entirely different level from ours, and an animal's idea of sexuality and sexual intercourse is nothing like our own.
So the big question is whether we're trying to make it illegal due to it actually being a 100% harmful act, or because it offends our moral sensibilities. I think the answer starts to become a bit more clear when people want to shift the subject away from the discussion because they find it "too creepy".