ScrewballAs for what to do about it. Do the leagues not have some sort of code of conduct? The only thing we can really do as a community is ostracize the offending individual.
To answer your question: RGL HL admin here. I can't speak for the prolander side, but we take toxicity (more specifically, personal player harassment) very seriously even outside of the game, and have banned multiple people from the league because of it. In fact, we banned about half a dozen people this past season for player harassment, primarily due to the use of slurs and witch hunting. As a side note, since we make all of our bans public, I don't have to hide that Scratchh has been banned from RGL for a while now for (guess what) harassment. Now, onto what I think...
It's very upsetting to me when I see this trend persist even after the countless threads people make denouncing this sort of behavior. You would think that more people would make a genuine effort to, as Screwb put it, ostracize the outwardly negative players from the community. I don't wanna name any names but there's definitely a handful of players that I'm surprised are still active and participate in the community, considering their controversial pasts. But no, only when someone goes out of their way to collect TONS of proof that they or someone they know has been facing this harassment extensively over a long period of time is there a brief knee-jerk reaction where everybody says "Hey man thats not cool," and we all forget about it in a week. I don't post much, but I've lurked for years and you can't tell me I'm wrong, because I swear this BS happens once every few months.
Thankfully, I'm lucky enough to have been given the opportunity to do something about it on a more official level. Like him or not, sigafoo has probably taken the biggest strides out of all of the leagues in the game's history to keep the community clean and free of toxic players, and all I can say is it feels good to play a role in helping achieve that goal. I hope others can take this example that he's setting to heart and begin making more of an effort to detrash the community.