But zoophilia is not about consent at all!

Scientists use dummy ostriches to collect sperm. Ostriches approach and... use the dummies, by their own volition.

If there was a human in there, it wouldn't be very different from the perspective of the real ostrich. So it'd be technically possible to consensually bottom an ostrich.

But why the fuck would you do it?

This is what people actually despise about bestiality. It's a gut feeling, before any rationalisation

Edit: you could very much argue that the ostrich dummy method is still non-consensual as it involves some form of trickery. But, regardless, I think it's telling that people would treat it differently depending on whether there was a human in it or not, even though from the animal's perspective there is no difference.