The longer a thread goes on, the more of those who don't really have strong opinions drop out - either because they feel they have nothing to add, or, have been jumped on by one side, with selective quotes, and driven out.
So ultimately after a few pages you just have those who are fully invested in arguing - either side - about whatever the topic has become. These are generally those with the more extreme views, and the time to sit at their PC, with the topic on their browser hitting refresh so they can post another self-satisfactory argument.
It just concentrates as these people try to drag the arguments into whatever their pet subject/gripe of the day is until someone lets slip their real views and the thread gets locked.
I get it, I like arguing too, and often I don't like when "people on the internet" are wrong. But I've learned its best to just not engage. My opinion is rarely changed, and theirs certainly won't be (especially those who claim "hey, I'm open to debate, and to other views" when they clearly aren't). Life is just easier when I (try to) ignore such topics.
As for what admin can do - honestly I have no idea. One mans free speech is another mans crossed line. And you can't just have "free speech" because again.. its easier for extremists to kick out moderates than it is for moderates to kick out extremists, so it inevitably goes south pretty quickly (like twitter lol). I appreciate its a very difficult task, and frankly I'm surprised there isn't more "drama" here - or maybe I've managed to keep my head in the sand for once?