The most horribly evil people are those who are stupid.
Gaining intelligence is easy. It means recognizing yourself, being attentive to your surroundings, and working toward a goal, even if it's selfish.
But it's the most evil thing in the world to recognize your own incompetence, turn your eyes from it, and become a burden on everyone else around you. To continuously make the same mistakes on purpose knowing someone else will fix them for you. To refuse to take responsibility for anything that happens. After a certain point, logic cannot be ignored. If you are logical, you will make the right choice even if you don't want to.

For stupid people, those who dismantle logic, that doesn't work. It's chaos. Stupidity is the most powerful and evil power in the entire world. It's all-consuming. It's addictive, it spreads faster and more aggressively than any disease, especially if it appeals to humor - That short-termed, feel good sensation that convinces you nothing is wrong because you can laugh it off.

Stupidity can be cured, if the participant is willing. But to be willfully stupid is evil.

I've met these people. So have you. They're not the people who disagree with you and debate the merits of something, or can hold articulate discourse on matters. They're the ones who dismiss them entirely.