Does this give you a right to do that??

if someone is a killer and and kills people in a country does that give them a right for that country to then do the same thing and kill them too.Like what happened with the iraqi people and the american people.The (bad)leader of iraq killed lots of people in america but then america(bush)fought by killing millions more then the iraqis did.I think this could have been handeled in many different ways but people who arn't educated fight with force that goes for the iraqi leader too.what do you think and please if you don't know how to be diplomatic then don't bother answering.