I rank high in IQ tests and I didn't fall for Marxism, or any other conspiracy theory like that.
It would not be wise to fall for these things, what with the invasion of the Reptilian alien race that put fluoride in the water to control our brain waves so that the Illuminati would conquer the Council For Foreign Relations, so that Cthulu would be awakened and stage another series of fake moon landings.
Oh, by the way, John F. Kennedy was shot by 21 Mafia gunmen.
I’ve never claimed that all or even most intelligent people fall for stupid ideas, merely that as a group they don’t seem to be noticeably any more resistant to them than those who are less intelligent.