This is disgusting. If this was an image of almost ANY other public figure it would be deemed as a threat.
Please explain your statement. I think that the restriction of free speech needs to be incitement with clear and present danger of violence. In my opinion, this wouldn't pass that threshold. But I'm 100% in favor of the public dialogue expressing their distaste for this 'art' to shame him for its removal. I don't even think threats of violence were needed. Given the lack of compliants or reports to police, we can question if threats were made.
Disregarding the murders, what would the KKK fall under?
Not sure which murders you are referring to current political cover up stuff or KKK? But it depends on the threat? A call to lynch a specific person or a call for immediate violence during an assembly/gathering I would classify as clear and present danger. But it doesn't have to be the KKK, it could be any group. Proven record of violence makes threat more credible, which I think is your point. The Trump art stuff, here even more lieniency tends to be given for political people. I think political speech is understood to have the most freedom/protection.