RICO exists. If the criminal activities were systematically prompted by a group, they can be sued and all their members may be prosecuted for these crimes, especially their leaders.
RICO is a pretty narrow tool, as it should be. It also isn’t based on group membership, it’s based on involvement in the planning / sponsorship of illegal activities.
It wouldn’t matter how many Hackernews members started coordinating bank robberies; RICO wouldn’t magically allow for the rest of the Hackernews user base to be prosecuted.
Sure. But if Hackernews had a hierarchy and a membership system in which lower-ranking members would do criminal acts organized by their ranking superiors, the organization could be sued under civil and criminal RICO, and then dismantled. While not all members would be prosecuted, a very large amount could be, and the subsequent criminal investigation would make it possible to indict a good proportion of the rest. It would also mean that even lower members could have been prosecuted based on their assistance to various criminal acts.
It is indeed a narrow tool, and yet can be applied to organizations such as the KKK.
I think your problem here is not so much that you don't know what RICO is, as that you don't have a tight grip on what the KKK is. It is probably the case that many, or even most, Klan members are also members of white supremacist criminal gangs. That those gangs are subject to RICO prosecution (a major Aryan gang was taken down that way just last year) illustrates the problem with your argument. The enterprise itself has to be focused on the racketeering-predicate crimes.
So no, this is entirely incorrect.