The butterfly effects would add up and and any zygote formed would not be the hitler-as-we-know anymore, since it would be a different combination of sperm and eggs.
Who needs guns when you got a time machine? Don’t like your highschool bully, just bump into their parents back in time. Or you know, “bump” ( ͡° ͜ʖ ͡°) into their parents.
Unpopular opinion.
Humanity is going to generate tyrants until we vaccinate everyone with a sense of morality and even then, we’re going to have problems with dark empaths starting shit as long as we think child soldiers can be saved.