Matthew Henry John Bartlett

Who thinks they’re not open-minded? Our hypothetical prim miss from the suburbs thinks she’s open-minded. Hasn’t she been taught to be? Ask anyone, and they’ll say the same thing: they’re pretty open-minded, though they draw the line at things that are really wrong. (Some tribes may avoid “wrong” as judgemental, and may instead use a more neutral sounding euphemism like “negative” or “destructive”.)

When people are bad at math, they know it, because they get the wrong answers on tests. But when people are bad at open-mindedness they don’t know it. In fact they tend to think the opposite. Remember, it’s the nature of fashion to be invisible. It wouldn’t work otherwise. Fashion doesn’t seem like fashion to someone in the grip of it. It just seems like the right thing to do. It’s only by looking from a distance that we see oscillations in people’s idea of the right thing to do, and can identify them as fashions.

[from Paul Graham’s essay What You Can’t Say]

You might also enjoy his list of idea-supressing labels.