An impulsive gunman taking advantage of chance doesn't make emotional sense if you're certain the Commies are at the gate.
For others, JFK's death had to mean something. It couldn't only be an attention-thirsty *expletive* simmering away at a temp job. It has to be part of all the intrigue that comes with being a United States president surrounded by political enemies and friends who all want him to do something besides what he's doing.
The conspiracy theories really took hold and achieved sustainable cultural velocity in the pursuit and aftermath of the Vietnam War. The Pentagon Papers revealed an actual clampdown on the truth about that war. We'll never be rid of it now because it's part of the national discourse. True or false, people are going to believe what they want to believe. And this far on, it has no real consequence in people's lives. Compared to the issues that impact us nowadays, the JFK assassination is something to knock around over drinks.
Lee Oswald alone with the mail order rifle in the Book Depository window? That's certainly what I think. But when I lived in Dallas a decade or so ago, my grandmother came out to visit the Texas family, and we took her to the Sixth Floor Museum in Dallas. I stood with her right beside the window, the actual place set up the way Oswald left it, the place where he took his three shots and changed the course of history.
And my grandmother who had lived through the entire thing looked at me and said, "I still think they took him out."