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.
Without the Holocaust, there’d have been no international horror over the atrocities of concentration camps, gas chambers, human experimentation, genocide. Anti-Jewish sentiment was rampant around the world.
Progressives made a lot of progress off the back of WWII, and the anti-fascist sentiment in the US that survived until the greatest generation died and their grandchildren took over. It’s entirely possible that, without WWII, the fascism we see in the US today would have happened much earlier, and we’d have run our own concentration camps.
Ironically, the people who probably would have benefited most from preventing “Hitler” would be the modern Palestinians, because without Hitler, Israel would not exist today, and it wouldn’t be carrying out a genocide.