Ah, but you missed the point! Some time travelers already have taken care of evil tyrants who would have been worse that those three, but the Universe will not be denied, and Stalin, Mao, Pol Pot, and Hitler rose to take the place of those who were removed from history. Didn't you see the Outer Limits episode where a time traveler went back to kill Hitler as an infant, but it turned out someone switched babies in the end?
"Didn't you see the Outer Limits episode where a time traveler went back to kill Hitler as an infant, but it turned out someone switched babies in the end?"
Oh, I forgot about the surprise ending. More subliminal predestination to drive ideologocial pseudoscientists batty.