It's perfectly rational to believe in conspiracies. When something happens that seems impossible, it's natural to look for a human explanation - and if the CIA can try to kill Fidel Castro with an exploding cigar, or Richard Nixon's boys can bug the Watergate Hotel, why wouldn't the KGB shoot John F. Kennedy and pin the blame on a chump called Lee Harvey Oswald?
Of all the conspiracies, the one against JFK is the most appealing because the subject was so attractive. President Donald Trump knew what he was doing when he allowed 2800 files to be released on the assassination, a crime that in popular memory felled the strongest President in an era of the highest ambition.
Kennedy pledged to fight communism and go to the moon. The playwright Tennessee Williams said he was almost "too attractive" to be President. There was a conspiracy of sorts to hide images of him limping about on crutches, one symptom of many illnesses, which meant that when Oswald shot him dead from the window of the Texas School Book Depository, the public was left with an impression of a virile leader felled by a "magic bullet". There had to be an element of magic in it because the Kennedys were cursed by bad luck: first Jack assassinated; then Bobby, shot in a hotel pantry; then Ted's car spun off a bridge at Chappaquiddick Island and his female passenger died; then Jack's son killed in an airplane crash.
Coincidence? Can fate really be that cruel? Yes. It can also be perversely kind. The assassination of JFK pickled his memory in aspic: black and white photos of a brilliant young man full of potential. Had he lived, however, Kennedy might be remembered as a byword for disappointment. Vietnam would still have happened. The riots would still have happened. Nixon would probably still have won the 1968 election.
And in retirement, Kennedy would've seen several birds come home to roost, such as his alleged affair with Judith Exner, the mistress of gangster Sam Giancana. Imagine JFK in the 70s, frail, divorced, disgraced. If conspirators had wanted to destroy Kennedy's myth, they'd have let him live. But they didn't make that choice - as Trump's data dump pretty much confirms, there were no conspirators. Just a loser with a gun.