There is a new view in biology that accepts that humans have introduced new species and there are many examples where mass killing just won't work anymore.

http://e360.yale.edu/feature/courting_controversy_with_a_new...

It's too late to go and kill all the cats. It's been tried in Australia for decades and it's a dismal failure.

It's arguable that trying to kill cats or rabbits or whatever now is just species Xenophobia.