Robert Nozick:

Utilitarian theory is embarrassed by the possibility of utility monsters who get enormously greater sums of utility from any sacrifice of others than these others lose . . . the theory seems to require that we all be sacrificed in the monster's maw, in order to increase total utility.

My point is that humans mostly act as though they are utility monsters with respect to non-humans (and possibly humans they don't identify with); they act as though the utility of non-sapient animal is vastly smaller than the utility of a human and so making the humans happy is always the best option. Some people put a much higher value on animal welfare than others, but there are few environmentalists willing to say that there is some number of hamsters (or whatever you assign minimal moral value to) worth killing a child to protect.