Really interesting! I would definitely agree that belief in conspiracy certainly provides meaning. I’ve always suspected that the need to believe in things like this are the desire to impose order on meaninglessness. It’s more comforting to believe that someone has a plan, even if they’re evil, than to believe that the whole world is just chaos. Even if they’re evil, it’s easier to defeat one evil villain than impose order upon chaos.
I instinctively feel that we’re not at a place to offer refutations yet. As you point out, religious fundamentalists and creationists don’t respond to facts about carbon dating! I think a better strategy is attempting to prove that their life would/could be better and have more meaning without the conspiratorial crutches that they lean upon.