You are arguing against killing Hitler. You’re right that this sounds stupid, because it is.
But your whole post is really beside the point: there are absolutely, positively, beyond any doubt politicians who could justifiably be assassinated. Set aside guesswork about how such an act would have played out – the act itself would obviously be justified. It would in no way make you worse than Hitler, or even anywhere near as reprehensible.
“Oh you think killing literally Hitler would be OK? Think again”