The economic take on things is kind of interesting. While a 'bandit' personality causes harm to others in order to benefit himself, "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."
Essentially stupid people are dangerous and damaging because reasonable people find it difficult to imagine and understand unreasonable behaviour. 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. The bandit wants a plus on his account. Since he is not intelligent enough to devise ways of obtaining the plus as well as providing you with a plus, he will produce his plus by causing a minus to appear on your account. 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.
With a stupid person all this is absolutely impossible as explained by the Third Basic Law. A stupid creature will harass you for no reason, for no advantage, without any plan or scheme and at the most improbable times and places. You have no rational way of telling if and when and how and why the stupid creature attacks. When confronted with a stupid individual you are completely at his mercy.