The phrase you are looking for is...
"How would you have stopped Hitler?"
Again, what exactly does that have to do with anything? Asking that question doesn't justify war.
*does
So you're saying that a war that happened over 60 years ago, before you and I were even born, is justified because of 1 death?
You really have no understanding of what war really is do you?
Also, you're saying that the millions of people who died on both sides are justified because the main antagonist died at the end?
You truly are a sick individual.