If you've got this time machine, why so negative? Stop the assassination of the Archduke in August 1914, and there wouldn't have been a First World War at that time, and Hitler would just have been a painter with a few barmy ideas. And probably most of us wouldn't have existed either, since our parents would probably have never met each other in a different timeline.

It's a fun game, but totally meaningless, unless you are proposing to go round murdering people just on the suspicion that sometime in the future they might turn out to be terrible people. Would any of us be safe?