Stupid compared to what they would do if they had more detachment. Most people do things without thinking it's bad, and when you point those things out, they realize that yeah, it's bad, never thought about it before. After all, if everyone does things, it surely means that it's good to do so, isn't it ? I'm pretty sure I myself do a lot of stupid things without realizing.
And that's really the point of the topic, because this lack of detachment, on a larger scale, is why people followed Bosh in the anti-zod fury. Had they have more detachment they may have realized that Vasudans aren't their enemies, that the TV-war is over and done with, and that fighting a new and useless war wasn't what was gonna improve their lives and make a nicer world for their children. That's how they are stupid : they believe what they are told without detachment.
I admit my explanation is probably a little simplistic, but that's the best way I found to express my point of vue. So yeah, I think people are stupid. Most of them. On the other hand you have people that persist in thinking they are right even if you point things out, but that's an other subject.