I don't think you have any idea what you are talking about.

4chan has an extremely non-SJW tilt. I wouldn't be surprised if the SJW term itself originated there as a pejorative.

The site's founder, moot, had to cut all ties with the site as it turned into an angry mob. It's no longer a fun and happy place, there's an undercurrent of hate, fear, and misogyny.

To an extent, yes. However that doesn't change the fact that some of the mods are backing SJW causes, and banning because of it. They blew off gamergate because of all their noisy crap, in spite of the important things they were pushing for. /r/kotakuinaction has much of this information in the "best" post listing.

The whole property is poisoned. The mods are incapable of keeping a lid on the problem.

This is the same phenomenon that played out at Reddit where the leadership was hesitant to try and interfere with so-called free-speech issues, and would then wildly over-react when things came to a head.

The problem is that 4chan's tone has turned from "social justice", those incidents early in its history where people were genuinely trying to help others as internet vigilantes, to those that started antagonizing people, and later, to viciously harassing them.

A lot of people who wanted no part of that have left. This skews the community heavily towards those who don't leave, who enjoy that sort of thing.

I'm not saying all participants in 4chan are guilty, but the nature of that entity, as a whole, is the polar opposite of SJW.