There's a huge difference between a classroom environment or academic symposium, and an internet forum. Here, when people attack and take swipes at each other, discussion slides downhill so fast that it becomes an existential issue for the forum. Having HN not destroy itself the way internet communities usually do has been the main goal here since pg created the site over a decade ago, and the guidelines here are written with all that experience in mind.
I used to think similarly about this to what you express, because I've always enjoyed reading about the sort of discourse in which devastating wit is exchanged. But eventually I realized that it doesn't translate into this context at all. This is a case of 'the medium is the message'. When you have millions of people who don't know each other all potentially interacting at the same time, the dynamics are so different as to be incommensurable with, say, small debates, literary journals, elite social events, and other places where the groups are small and highly cohesive. Here are some previous explanations about this:
All these politeness comments are a speed bump that distracts from the real issues.