I mod r/marvel and r/blackpanther and then I follow certain niche subreddits. The niche hobby subreddits are generally fine and cool (like aquariums, smaller video games, like monsterhunter, and powerlifting stuff).
But, dear god, it is so easy to click something and end up seeing the "popular" megasubreddits and it is just doomscrolling and really easy to get sucked in to seeing toxic shit over and over.
And each megasub has its own brand of toxic. Whether its depression, outright white supremacy, liberal white supremacy, women hating, man hating (the woman subs do the same thing)... if the "black only" type subs turn into militant hate white people toxic stuff.
It is just like if you get TOO many people... the toxic loud parts slowly take over until that is all that is left.
traditional forums like CBR, it is harder to build that toxic base becaues threads just build one after another. The loud minority kinda gets drowned out a bit.