But it was in the world's self-interest to remove him before he came after them. His actions showed the world he was incapable of abiding by civilized conduct (which also predates Christianity) and was a threat to everyone.
Was Hitler wrong? By whose standard? Yours? Or did his actions simply militate against the universal law of natural selection, in which case he can't be right or wrong, just extinct? What is "civilized" - here is another word that suggests a standard. You keep using them. Who decides the standards of conduct and which ones are right and wrong? Is there a right and wrong?