It is unclear how this could be enforced in the internet domain, but maybe the website could have huge fines levied against it or criminal charges levied against the founders (so not the posters) if its possible to prove violent intent. Its also not a very slippery slope. We have hate crime laws, but they are notoriously hard to prove. I imagine violent intent on the internet will be similarly hard to prove and only be applied to the extremely obvious cases.
Its also a bit weird. Nobody made a huge deal about PornHub (from what I can tell) being forced to take down tons of content due to Visa, because guess what. Its hard to disagree that the source of a lot of content on PornHub is troubling and very likely illegal. This isn't that much different from what Amazon and other companies are doing to Parler. The intent of a lot of posters (even if its a minority) seems to be to incite violence. Parler actively didn't try to monitor the content and boom, it got taken down. I imagine if PornHub didn't make a good faith attempt to remove a lot of content, we'd have seen Amazon (or whoever hosts PornHub).