Its a danger to society. And it is not once. It is after 3 times I believe and I also think it is if it kills someone (or after 3 times the owner is responsible). I am not exactly sure, but animals are trained certain ways. If they killed then it can happen again soo better to kill it before it kills another human again. Also to bring precaution for next time that the owner should take care it it better or suffer at least this loss (of his animal).