They just end up sounding stupid and contradictory. Example, here they decry zoophilia (sex with animals):
“It is shocking. It should be illegal in every state,” said Stephanie Bell with People for the Ethical Treatment of Animals. “It’s not a laughing matter. Even in cases where physical harm doesn’t occur to the animal, it’s still cruel.”
Um ... so no harm is actually done. But it's still bad. But it's not harmful. But it's still wrong. But ... uh ...
*Mind fizzles*
Another point one needs to add to PETA's ever-growing list of logical failures: nothing is universally bad or wrong. Nothing. Call me optimistic (or insane, either way, they do tend to correlate ...) but I cannot think of a single act that's usually wrong – pedophilia, incest, zoophilia, whatever – that can't be morally acceptable under certain circumstances. The fact that an act is usually wrong or cruel does not make it so 100% of the time. There's always grey area, no matter how small it may be.
Besides, I've already stated my opinions that sex with animals, while unsavory and frankly strange, is usually harmless to both humans and animals. You simply cannot rationally condemn something that is specifically harmless, regardless of how you feel about it.