So impotent that they never walked into a synagogue or mosque and shot up a bunch of people. Oh wait...
Leaving that aside, banning white nationalism does not prevent Facebook from banning other content it considers extremist in the future, regardless of what you see happening any time soon.
Weak meme, 2/10.
For example, if the U.S. government's tax revenues were much lower in the 1960's, would they still have invaded Vietnam? Perhaps not entering Vietnam would have saved far more lives than are lost to domestic mass-shootings.
My main point is simply that causal relationships between policies and (various definitions of) harm can be highly speculative and messy.
We went to war over it.
Should people be banned from advocating for or against such policies on Facebook? I mean, if one advocates for, it would hurt one set of people. If one advocated against, it would hurt another set of people. If you say we must raise taxes, you will be repugnant to Libertarians. If you say we must lower taxes, you will be repugnant to welfare state proponents. Should we just limit ourselves to posting cat pictures on Facebook? Nobody would disagree with cats, right? Right?
But they do. Not all of them in synagogues and mosques of course, some of them do it on stadiums, night clubs, buses, trains, buildings, and some use explosives, poisons, cars, etc. But adherents of all ideologies above committed acts of murder. So, by your logic, every adherent of such an ideology should be banned. Or just those that visit 8chan? It's hard to tell these days.