ignorance and stupidity (And remember, I’m illustrating a distinction, not offering a definition.):

Ignorance is when you do something out of a lack of knowledge. Since no one can know everything, there is no shame in being ignorant.

Stupidity is doing something in spite of knowledge or better judgment. We’ve all seen or heard stories about criminals robbing a store with a policeman standing right there.

I’m not sure whether there’s any stupidity involved in signing up for an MLM, but ALL of them take advantage of a prospect’s ignorance, which eventually impacts a person’s judgment. So the “drain one’s IQ” remark is well-taken.