They feel that someone communicating ideas that challenge theirs is such an affront - such a disturbance to their self-assured sense of personal rightness and superiority - that that person's death is a good solution.
Or to put it another way - they're like this because they're confident they won't receive comeuppance for being so. It's like a "what you gonna do?" frolic.
It's like an entire generation is suffering from a serious emotional malady. It feels like the entire society got derailed morally and ethically. What happened? Did education fail everyone that much?