They put on a good show. Real racist people post videos of the f&#$ed up things they do to others that I won't even describe here. They know better than to use a clear-web site especially one using a CDN to show off their behavior. Those forums are on Tor.
4chan is nearly all angsty edgy teens on their cell phones at school trying to act tough and edgy and even they get arrested when talking tough about cops or pulling shenanigans like defacing or vandalizing property to be cool. That's a different interesting topic. Search youtube for all the 4chan unstable kids getting arrested. It's on-par with all the unstables vandalizing Tesla cars.
Well, I believe you that there are lots of kids there that try to seem racist for 4chan cred, and I guess people would know not to post videos of themselves doing those illegal things.
But I remember they had stuff like "n*gger chimpout" compilation threads, and whenever people talk about what they blame on Jews, they seem to be actually bitter and angry, so they do seem legitimately racist. I wouldn't be surprised if there was a lot of overlap with the people who do commit those acts of violence you're talking about, but even if not, I don't think you could say they're not real racists just because they don't post videos of themselves committing violent hate crimes. The board is just diluted by low-effort threads and bait by users of other boards.
But I remember they had stuff like "ngger chimpout" compilation threads*
I guess that's why we don't really see quite eye-to-eye on this. I've seen all those threads and to me that's just kids being edgy because they know it triggers or activates people. Every group has it's trash and they are just singling out one specific groups shenanigans. The same behavior can be found of every breed of human and they would post it if it was edgy to do so. My breed has no shortage of dumb behavior but when it's posted people feel comfortable laughing at it thus it's not edgy or taboo enough.
As a side note, most of the kids on 4chan are also here on HN. They talk about this site, its users and dang all the time. I'm sure they are not happy that I am pointing out they are just LARPing.
Compilation threads like those seem to me more like ways to make each other angrier and more racist. I think they legitimately just hate black people. Like, there's definitely some element of smug self-aware memey edginess about being racist, but there's also unironic vitriolic racism. But yeah, I guess we just disagree here on this.