Earlier quoted context omitted.
You're trying to generalize a useful rule ("shun white supremacists") but it doesn't work in this case. I don't think we need to, either. We're not robots. We can shun white supremacists and leave everyone else alone. This isn't a slippery slope, it's just good sense (no more white supremacists, hey!). Humankind will get along just fine if we tack on that one extra rule and all follow it.
Good thing the definition of white supremacist is commonly agreed upon and noncontroversial and absolutely isnt subject to definition creep :)
Murder now, for some, includes abortion.
Censorship now includes, for some, private companies removing bad actors from their private systems.
Come on, that's lazy to dismiss it that way when society literally changes all the time.