I feel kind of guilty raining on everyone's parade but Reagan and Kennedy both benefit from rose tinted glass syndrome in most peoples' eyes. Kennedy gave some great speeches and really galvanized the US in things like the space race, but he was also responsible for startomg the escalations in Vietnam.
Kennedy had planned to back out of 'nam after the next election, but that idea was cut short.
Still, I think if Kennedy had lived, his ugly side and behavior would have come out, the press would have stopped turning a blind eye to his shenanigans, both personal and political. He was pretty much the last president where the press more or less decided to gloss over things, after that the press developed much more of a cut throat attitude toward politicians, which is actually a good thing.