Being a culturally significant figure in black politics isn't a good reason to keep someone who's attempting to incite mass murder against a minority religious group on a forum like Facebook. You mention the picture of him standing next to Obama: that's actually a fairly famous photo. Obama explicitly rejected and denounced Farrakhan [1] when he ran for president, and in an ironic turn of events (considering the nascent alt-right's smear of Obama as being supposedly-Muslim) Farrakhan later accused Obama of being "the first Jewish president" who was "selected before he was elected ... [by] rich, powerful members of the Jewish community." [2]
Silencing Farrakhan in general on Facebook is a consequence of silencing his particularly horrifying views about Jews and removing access to the platform he uses to spread them. This isn't because he's a culturally significant black man, it's because he's an anti-Semite. The others de-platformed along with him are not fellow black leaders, they are racists and conspiracy theorists who are similarly dangerous and have similarly used these platforms to spread hatred to millions of followers.
> The original post I was replying to didn't specifically mention antisemitism, it said "racism" is justification for banning someone.
While on the one hand you're claiming to only refer to the hypothetical question of a black leader who is anti-white, you also specifically defend Farrakhan's presence on social media, and question whether Facebook should be able to ban specifically him for his anti-Semitism; for example:
> I don’t know how old you are, but I think you’re being ignorant about the full spectrum of what Farrakhan represents. He co-organized the Million Man March, which was a defining event in the 1990s, much like the Ferguson shooting is today . . . Maybe the anti-semitism alone warrants a ban. Maybe any one of his extreme view warrants a ban. But it’s very problematic for Facebook, a company with almost no black leadership, to be making that call.
If we were talking about a hypothetical black leader who was anti-white (and whether you can call that racism is, IMO, up for debate), and who was not virulently anti-Semitic, I would definitely agree that's a harder question to answer; I'd probably be against banning someone like that, for reasons that are long and complicated and that you'd probably agree with. That isn't what happened here, though, and it's not who we've been talking about: we've been talking about Farrakhan, who's in both my opinion and Obama's opinion fairly indefensible.
[1]: https://blogs.wsj.com/washwire/2008/02/26/obama-denounces-fa...
[2]: https://www.splcenter.org/fighting-hate/extremist-files/indi...