I suspect it's simply that most jew-hating etc. jokes are unmotivated unless you hate jews. If you don't hate jews you find the jokes unfunny and tedious and stop browsing, and if you do you join in. The origins of 8/4chan barely matter.
It doesn’t require hate, just not giving a shit about people’s feelings.
What happens in an environment like that is that people that _do_ hate start to feel welcome, and eventually drive out the people who were just in it for the lulz. Or radicalizing them as well.
And if you want someone to care about your feelings, the first step is never to tell them they are garbage.
Loving your enemy is a worthwhile strategy.