It's not some theoretical 'divisive', you can read how these threads go yourself, including this one. The meta discussions also make these a lot worse so it's hard to blame this on some 'small number' of people.
I think by playing the brinksmanship card of "there can be no level-headed discussion" you inadvertently discount a lot of perfectly coherent and important digression, on both sides. If every HN thread resorted to this logic, nobody would want to use the site.
The brinksmanship card of HN is the reverse of this framing: There must be level-headed discussion. To wit:
>The most important principle on HN, though, is to make thoughtful comments. Thoughtful in both senses: civil and substantial.
Some comments that clearly break the rules should be removed by the community. But that should take multiple downvotes.
The flagging just allows one or two people to remove a part of the discussion, and we rely on other users to view dead or flagged comments to “rescue” them