Or, maybe it's not? I don't see that that follows. Yes, there's the slippery slope argument that someday a host could make a decision we don't agree with. But (1) hosts do that anyway, all the time, and (2) if fucking white power racism isn't on solid, level ground above the slope, then what else could be?
The solution to private sector choice about hosting and distribution of controversial content can't be a blanket protection for all speech. The first amendment is about public law, because of the reach of the government and the potential damage from abuse.
The solution in the end really can only be a case-by-case determination, individually by every host, as to what they are comfortable seeing on their systems. Which is exactly what we have here, even if CloudFlare's internal process was exposed as messier than we'd like to see.