What's the correlation to education level? I find it hard to believe that well educated people don't know how to validate sources and apply proper reasoning. The spit test tells me this is the case, as I know a lot of Ivy Leaguers that are not dumb as rocks in the ways you describe. (Lack of common sense is something else I think). Everyone I know who follows conspiracy theories is uneducated.

Also, do highly-educated countries like Finland have this same level of stupidity?