AskScience is a default sub, I think, and they've survived alright. Interestingly, AskHistorians asked to not be a default sub-reddit for precisely the reasons you've given.

They have something like 500 moderators though so there is that.

They used to ruthlessly remove everything without an academic source, however interesting - these days I feel more and more fluff is getting through.

I think you are very correct.

Maybe one of the nice things about UseNet was that you could only be signed up for a forum that you explicitly looked for? That at least forces the trolls to go out of their way to interfere with general-interest sections, not just go after them out of laziness.