I don't think they're stupid, but if someone identifies themselves as "a Republican" or "a Democrat", as opposed to "the Republican party best fits my views", or "I'm a registered Democrat", I pretty much write off any chance of having a decent political discussion with them.
A large segment of the population follows politics the way they follow football, except without even watching the games, just the commentary and opinion pieces afterwards.
Smart people also triage their time so as to not waste it going down likely unproductive avenues.
But it's just a numbers game; there are invariably going to be people a level above me intellectually who this will filter out. But I can live with that.