People promoting violence usually means targeted violence. Proposing violence against a specific person or group of people. A protest that happens to have people in that become violent and then those some people posting online is a completely different situation than a bunch of Nazis saying we need to exterminate the Jewish people.
Allowing violent people to post online is fine. Allowing them to post violent content is bad. I don't care who the person is. I care what they post. As long as they're not advocating harm to a specific person or group of people it's fine.
I'm okay with people saying racist things from a free speech perspective (it's still despicable). I'm not okay with them saying people should go burn down the synagogue in downtown Seattle.
TBH, this point is poor. Violence and therefore promotion of violence are simply necessary in some situations. The former is even ingrained in the U.S. constitution.
Plenty of comedic and satirical shows have been censored for racism. Plenty of violent forms of entertainment have been censored. This campaign is also calling for the censorship of anti-vaccination and climate denialist views.
I've done a bit of volunteer work as a censor (moderator) and I'm not opposed to censorship. A flippant/morally self-righteous attitude towards censorship is a red flag though.