People on HN enjoy criticism just fine, but they don't particularly enjoy standing next to a spigot of feces. The problem is that vitriol and excessive emotion skews debate. It makes the debate about the emotion itself, rather than about the issue at hand. When people get into a shouting match their brains shut down and people stop arguing rationally (the fight-or-flight response kicks in, blood starts being withdrawn from the extremities and some of the higher brain-function areas, the reptile brain starts taking over, and it becomes much more difficult to admit being wrong or that the other person might be right). This sort of thing is not helpful if the goal is productive rational debate.