Killing Hitler would be (relatively) easy. What stops us is our knowledge of time travel theory, at least as presented in fiction. That is, 1) we can’t change history at all (accidentally killing the one person who could have helped Adolf get into art school) or 2) we can only make things worse (Hitler’s death leads to Stalin controlling the world) or 3) we can change one timeline but it doesn’t effect the original timeline we came from, it merely creates another tributary in the time stream.
Your time machine takes you back to Dallas, November of 1963. You have the ability to prevent JKF’s assassination. (For the sake of simplicity, we won’t say if you are preventing the acts of Oswald or persons unknown of an unnamed conspiracy.)
Do you?
Okay, ignoring the Twilight Zonish silliness ofd the premise, the answer is:
Yes, of course I’d try to save Kennedy, but NOT because I have any Oliver Stonesque delusions that Kennedy would have gone on to do great things. I think Kennedy would have made most of the same mistakes Lyndon Johnson made (getting the U.S. bogged down in Viet Nam), but wouldn’t have ANY of Johnson’s great achievements (civil rights).
I’d try to save Kennedy for the same reason I HOPE I’d try to help anyone in mortal danger: because it’s the humane thing to do. The possible fallout is irrelevant. Does a doctor check out a critically wounded patient’s criminal history before treating him (“maybe I’m saving a future murderer… maybe I SHOULDN’T treat him!”)? No. The doctor does his best to save everyone, the good and bad alike.
My gut tells me that the world would NOT be notably better off if JFK had survived. But he was a human being, and if I could have saved him and his family from that tragedy in Dalls, I would have.
Except for incredibly extreme circumstances, I think any hypothetical time-travellers should keep their hypothetical hands in their hypothetical pockets.
We can’t know what it would do to the timeline–not only would Kennedy have continued in office, but the ripple effects would continue long after. Maybe these would be be good, but maybe not. If nothing else, we know that we didn’t manage to have World Wars III and IV over the past 38 years–if you change history, you might change that as well.
I can’t agree with astorian’s comparison to a doctor with a single patient. The stakes are conceivably much higher–it takes one US/Soviet nuclear exchange, either under Kennedy or a changed successor, to kill off more people than World Wars I and II combined. So I think I would choose the devil I know over the devil I don’t, and refrain from intervening.