From TNG Episode 9 Season 5 : A Matter of Time, we have Picard saying the following to Rasmussen:
Yes Professor I know... What if one of those lives I save down there as a child who grows up to be the next Adolf Hitler or Khan Singh? Every first year philosophy student has been asked that question since the earliest wormholes were discovered..."
While this quote might have reminded and delighted fans of Khan's name/place in Earth's history, the canon however shows that Khan really didn't really have so much comparable blood on his ledger. In fact, it even indicates that his reign of tyranny was actually lacking massacres.
So wanted to know if there was something else that elevated Khan to Hitler levels of infamy to earn a place in Starfleet Philosophy discussions!