If you’re going to build a time machine and assassinate historical figures before they can do the nasty shit that made them infamous, why start with Hitler? That’s too obvious, and too easy.
Me? I’d suggest starting with Paul Graham, Elon Musk, Peter Thiel, Jack Dorsey, Marc Andreessen, Mark Zuckerberg, and Curtis Yarvin. You won’t be going back that far, so I figure you’re less likely to fuck up the timeline. You might just prevent Silicon Valley from becoming the intellectual and moral equivalent of a Superfund site by preventing the founding of Y Combinator, too.
You might also prevent both Trump administrations and the Biden administration. Maybe. Not that I’d suggest a direct preventative approach. After all, if you went back in time and whacked Hitler, you’d probably come back to find out that Godwin’s Law is about Heinrich fuckin’ Himmler instead. Unless you also bump off Himmler, Göring, Goebbels, and the rest of those goose-stepping assholes. Good luck with that, incidentally.
This is probably why C. J. Cherryh’s Morgaine cycle probably had the most realistic depiction of time travel in all of sf in its backstory. In those novels, the alien qhal had found stargates that also let them travel through time. Going backward in time was forbidden, but somebody did it and caused a reality dysfunction (to borrow a term from Peter F. Hamilton) that permanently fucked up qhal-controlled space. So, when humans found a Gate for the first time, they decided it was necessary to create a suicide platoon to traverse every Gate and seal them behind them lest some other idiot decide to backtime (to use Cherryh’s term) and cause another reality dysfunction.
Of course, Michael Moorcock had something called the “Morphail Effect”. In his fiction, the past is read-only, and any attempt to tamper with it by a time traveller would get the traveller immediately and forcibly returned to their proper place in the timeline.
Then again, we seem to be living through a reality dysfunction right now, without any causes from sf. It’s not something we can blame on the gods, either. We did this to ourselves. We’re doing this to each other.
What the hell for, anyway? So some rich and powerful assholes can get even richer and more powerful? Fuck ’em. What have these people done for any of us lately?
Maybe we can’t just kill ’em all, but what’s stopping us from stripping them of their wealth and power? Why not make them spend the rest of their lives working on public infrastructure?