I'm not sure evil ends there. The 9/11 terrorists also died intentionally from their own actions, but mere insanity doesn't explain such a coordinated attack. It's just that they see their own death as a necessary sacrifice in a larger struggle. The same may be true for some mass shooters, especially the ones clearly motivated by racism or other bigotry: sacrifice your own life to take out more of the enemy. In their mind, it's probably no different than a soldier risking his life to defend his country. (Well, maybe that counts as delusion and is still insanity, but also evil.)
Yeah the 9/11 hijackers valued the mission over their own lives, which is usually considered a valorous attitude, except in this instance their mission was evil. And this illustrates another point: if you’re evil but not stupid, you’re going to be more capable which means you can do a lot more damage if you want to. We should prefer the evil to be stupid so as to undermine their effectiveness.
That being said, stupidity is still far more common than evil, so the damage done by the stupid-but-not-evil probably outweighs whatever damage mitigation we experience from the stupidity of evil people. (And it’s worth noting that many if not most evil people are quite stupid, at least in terms of common criminals.)
