Little kids form clubs and hatch secret plots and keep other little kids out. Archaic culture all over the world have secret societies with special rituals and methods of scaring off the uninitiated. I'm more than half convinced that humans invented language in the first place so that we could communicate our secrets in whispers instead of hooting across the clearing like chimpanzees.
So from that perspective, it would be surprising if there were no conspiracies in our own culture. I think that when people argue about conspiracy theories, the question is not whether conspiracies exist but how powerful they are, how deeply they reach into the centers of power, how willing they are to undertake criminal acts, and how easily they can get away with them.
I mean, everybody knows that the Republicans are colluding to try to undercut President Obama. That's so obvious, it would be ridiculous to try to deny it. But if somebody claimed that John Boehner was planning a military coup or an assassination, the most likely reaction would be, "Yeah, right. And would you like to buy this bridge in Brooklyn?"
In other words, the real line to draw is not between conspiracies and no-conspiracies, but between plausible conspiracies and implausible ones. In the case of the Kennedy assassination and a few other episodes, the stakes are so high and the events so shocking that it becomes very difficult to know where to draw that line. But I do think that what we're really arguing about here is not whether there *was* a conspiracy to kill Kennedy but whether it's plausible that there might have been. And that, I think, should be a legitimate subject for discussion.