Conspiracy theories are very curious things in that they are superficially ridiculous but can suck people in if they can get past that. And I think those things are related.
One of the best descriptions of God comes from a letter of Saint Paul: “He who accomplishes all things according to the intentions of His will”. It’s a marvelous contrast to human beings, who accomplish very little according to the intentions of our wills; our successes are usually only partial successes. And this is where the superficial ridiculousness of conspiracy theories comes from.
Conspiracy theories all assume hyper-competence on the part of the conspirators.
This is why it’s so hard to put into words why a conspiracy theory is ridiculous: it’s because of all the multitude of things which had to go right in order for the conspiracy to succeed.
This is also why it’s so hard to argue a conspiracy theory. Any one thing which had to go right can be explained away; it’s all of them put together that just get ridiculous.
I think this is also why, if one can get past that initial instinct to just laugh, conspiracy theories can suck people in. They’re a bit like mystery stories, but on steroids. As long as one considers the pieces in isolation, each one is a puzzle to solve where you get to match wits with someone really clever.
It’s that in isolation part which is so critical, though. There’s actually a similar problem when watching a long-running show like Murder, She Wrote. (A show I dearly love, I should add, and for me some formative fiction.) On any given episode, it’s reasonable enough that a murder mystery writer should happen to be present at the scene of a cleverly committed murder. That it happened 263 times defies belief. Hence all of the jokes about how Jessica is a serial killer who framed others for her crimes.
(It should be noted that the joke of Jessica being a serial killer is not viable given that almost every episode ends with the killer confessing.)
Large conspiracy theories are ridiculous because they’re like being presented the entirety of Murder, She Wrote all at once.