Talking about "banning" is a strawman, and pointing to impartial rules is an easy way to write off that they end up applied preferentially.

What I'm referring to is that the blue team has taken over the discourse of many popular forums [0]. HN has gotten better, but a few years ago it was quite hard to raise legitimate non-blue-flavored criticism without being downvoted into oblivion. Predictably, the only red-flavored comments being left were then lower effort, which would then get flagged to death.

So then people with moderate red-flavored views are left to go find different discussion forums if they want to express those views. And the places they end up have been similarly "claimed" by the red team, and are thus analogously tolerant of red team extremism.

Now rather than experiencing events like Christchurch primarily as a shared tragedy in which humans were killed (eg holy fuck what are we all doing to each other), the tragedies are mediated by political groupthink. To avoid having to distance themselves from their extremists, the home team caricaturizes the reaction of the other team. This creates cognitive dissonance which normalizes the extremist behavior rather than condemning it.

[0] At least from our perspective here. I'm certainly willing to posit someone could have a mirrored view where their popular forums are ever-more red-team flavored. This fits into my point.