I read about Carlo M. Cipolla and his Laws Of Stupidity a few weeks ago, and his definitions really stuck with me.
Stupid can be given a definition that doesn’t have an explicit value judgment attached.
A stupid person is a person who causes losses to another person or to a group of persons while himself deriving no gain and even possibly incurring losses.
He goes on:
Essentially stupid people are dangerous and damaging because reasonable people find it difficult to imagine and understand unreasonable behavior.
An intelligent person may understand the logic of a bandit. The bandit’s actions follow a pattern of rationality: nasty rationality, if you like, but still rationality. All this is bad, but it is rational and if you are rational you can predict it. You can foresee a bandit’s actions, his nasty manoeuvres and ugly aspirations and often can build up your defenses.
OK, maybe the implicit value judgment is still there.