If there's no difference between humans and animals then yes nobody could be surprised with genocide.
That's the logical conclusion from this premise.
The theory of evolution really says humans and animals have no biological differences in some kind of superiority.
But the theory doesn't says this premise extrapolates biology. Actually both Darwin and Wallace recognized the problem of consciousness in ToE. Wallace spent the rest of his life trying to find a paranormal explanation about consciousness. He is not remembered as Darwin because this.
Of course the majority of humans know we are more than just biology. That's why this biological premise is not acceptable in law.
But some people think humans are just biology. This view it's not from science but from scientism. This cultish view is very wide spread today.