One of the points Jennings made was that most people want to believe in a conspiracy because it is simply too much to fathom that a lone nut like Oswald could kill the most powerful man and the world and affect human history in such a way. There simply must have been something bigger, because it shouldn't be possible for one person to have caused something with such massive ramifications.
The fact is that to this day there is no physical evidence of a conspiracy; Oswald could, and did make both shots, and he did so alone.
People who point to the grassy knoll have never been to Dealy Plaza. The grassy knoll isn't some vast patch of land, its a small lawn about the size of my front yard. Zapruder himself would have been startled by the shots since he was only a few feet away.
These days I steer real clear of '9/11 Truthers' who think the WTC was brought down by explosives and radio controlled jetliners.
I listened to one nutbat at a New Year's Eve party here in SF a couple years ago go on and on to anyone who would listen about Bush's grandfather meeting Hitler on a Nazi zeppelin, the Trilateral Commission, Osama visiting the Bush ranch, timed CIA explosives planted by Marvin Bush, radio controlled jet liners, "Haven't you seen 'Loose Change'? Well, let me get your email so I can... Hey, where are you going?"... Just fascinating. He truly believed it. Really made everyone uncomfortable. He's still out there believing it, I bet.