What does it mean to judge a belief as "idiotic"? Surely not that every believer is ipso facto an idiot. That would be far too strong. Perhaps it means that they are idiots in the respect that they hold that belief (allowing that this may be outweighed by insight or intelligence in other respects). Or perhaps it's just a general disparagement of the belief in question, and doesn't really have any clear meaning (or implications about believers) at all?
Take as an example Young-Earth Creationism, or perhaps astrology. (If you believe in one of these, then pick the other. I'm hoping that nobody believes both!) These strike me as prime examples of idiotic beliefs. Does it imply anything about the people who believe them? Should we say that anybody who believes in astrology is, as a person, idiotic in that respect? (I guess I'm inclined towards an affirmative answer, but I'd like to hear what others think.)