Yeah, why do you think they made time travel illegal?  Because they have some idea what they’re doing and adequately plan for the future?  

Fuck no.  It’s because the entire Prime timeline was rendered completely inaccessible by one guy who has since spread to 1,489 other timelines, probably over 1,600 by now.

Every time you travel to the past a new world is created.  You can never re-enter your own past and change it.  You can only make a new one.  

Because of Hitler, our original past was lost to us and is now unknowable.  He’s the first time traveler, and the greatest criminal in history.