First off, the chimera ants were out to destroy the human race. That means survival, and the basic instinct of any animal, is that, especially that which is pushed to a corner. Secondly, there's no cheap trick in a battle, a defeat is a defeat. Wars are not fair. Tigers hide behind tall grass and attack from the back. Crocodiles hide under water. These tactics are not fair. Third, I'm not defending humans here, but, I won't defend the chimera ants either. Plus, if you remember, some chimera ants turned good only because the human parts of their body took over.