This wasn't really my experience. "Jokes" didn't lead people to becoming racist or white supremacist. What it did do though is make people who were actually white supremacist come in and try to spread their ideologies and win people over to their side, so they could convince a fraction, probably the minority of posters, to actually believing it, and eventually their numbers grew.

The idea that people turned into white supremacists because they made a few jokes is kind of a slipery slope argument.