I think as it is now leftism is an intellectual position, but historically I don’t think that’s always been true, when leftist movements saw more broad popular appeal like during labor organizing there were definitely dumb leftists.

The reason it’s in Republicans best interest to keep people stupid is that stupid people are much easier to propagandize to. Analyzing the information you’re receiving helps make you less likely to fall for blatant lies. (Leftists know we need better propaganda, but it’s also deeply cynical to think we need it.)