>>14126910When you catalyze your entire personality around being part of the morally superior tribe in a world of evil others, you lose the ability to empathize. You don't see people as individuals anymore, everyone is either identical to yourself or not human. Religious zealots of other faiths get the same way because when there are no other people to think about there's no reason to communicate, they literally start to lose theory of mind.
If you don't have real theory of mind you can't produce humor because it relies on simulating the stream of concepts in your head as if you were ignorant to understand if it will be funny to others. This is also why lefty memes tend to be giant walls of text. If you can't simulate another's thought process you assume complete ignorance and therefore feel the need to grossly over-explain the situation to bring the reader up to speed for the punchline. Their memes also tend to be hateful because the only humor people like this CAN spread is malice, not the joy of absurdity but the cruel sadism enjoyed when hurting another living thing.