There's a difference between discrimination and being treated like second-class citizens. Spectre was saying that if black people truly were second-class citizens, there wouldn't be a black president. He mentioned Aboriginals as people who truly were treated as second-class citizens, similar to how black people were treated for a long time. Not anymore though. He respoded to a post claiming black people were treated like second-class citizens.
Was his post ignorant? Maybe. Does it differ from some other posters' views? Sure. Is it outright purposely offensive and attacking and banworthy? Not in a million years.
If ignorance and differing opinions were banworthy, gaming-gaf wouldn't exist. Not to mention Spectre was being civil, which gaming-gaf also isn't.
TL;DR: Stay in the bubble if your opinion differs from the majority or you'll get banned.