Spencer didn't write that article. Colin Liddell did, for Spencer's white nationalist website AlternativeRight. Liddell claimed he was being ironic, by comparing the notion of a black genocide with the real white genocide he claimed was occurring in post-apartheid South Africa. However, what the "article" seemed to be clearly suggesting is that, if anyone should be the object of a genocide, it should be blacks, not whites. The last two paragraphs of this masterpiece:
Spencer proudly published this piece, until he concluded the heat it was attracting would undermine other projects he was working on, so he deleted it. Shortly after publication, Liddell contributed Is White Genocide Right?, which Spencer also deleted along with the former piece. This article actually was sarcastic, making basically the same "argument" as Is Black Genocide Right?
Both Spencer and Liddell are clearly neo-Nazis, from where I'm sitting.