You've just given me a weird desire to try talking people into flat earthism just to get a feel for how difficult it is. I'm holding off... for now!

I do take your point though, the world is replete with causes which more or less look like averagely smart or even smarter people talked into campaigning for something that is against evidence, sense, morality or reason - or all of the above - which are also probably (or provably) against their own interests. I'm sure everyone reading can provide their own examples but please don't. I remain unconvinced that this sort of persuasion scales neatly with intelligence, though.