Frankly, if you could go back in time and kill someone to change history, why cant you go back in time and not kill someone to change the future? Instead of killing jesus at birth as one poster suggested, why not approach him when hes older and discuss things with him, like the truth about the way the world works or something....or even hitler, teach him about the truth of other races, religions and creeds.
This approach assumes some predisposition to carry out the horrible atrocities that people have in the past. Our thoughts and ideas, and therefore our actions are shaped by our experiences in life - change those experiences and you will change the resulting person. Every one of us is the same fundamentally, our differences are differences of experience and experiences change our ideas constantly throughout life, and for this reason no one ever has or ever will 'deserve' to die. We should all strive for a world where killing is eliminated utterly, in all forms be it a personal feud or a massive war, we are capable of so much more.
