Have you ever actually seen a beastiality community? Do a search for one on Google, you'll get a feel people's motives and how they fetishize it.
People will often keep public diaries filled with their fantasies of mostly an absurd sort like dolphin ***********; sometimes they're personal accounts of a very terrifying sort like chicken ***********, where the animals are too small for safe penetration, so the animals thrash and flail violently, and often die from internal damage.
I got the impression that they aren't really into zoosadism per se, but really view animals as a kinky sex toy. In their universe, some people **** pies, other people **** chickens, what's the difference?
So, yes, I think there is a very strong objection to beastiality not only because its non-consentual, but animals are tangibly and severely harmed or killed in the process.