Yes, a knowledge of “proper English” can be beneficial. But it turns out that speakers of other varieties—or other languages—are totally aware of this, not being idiots: if these speakers have access to resources that allow them to acquire “proper English,” they almost definitely will. (There’s a lot of literature to support this, by the way—I’m not just blowing smoke out my ass like I usually do.)
The implication that people who aren't speaking perfect General American clearly just don't know how and would happily adopt White Man's English if only they had access to better education seems... a bit off, to me. Especially in the context of cultural slang.
Kind of ties in to something that's been bothering me lately: racism as a binary value. As in, if you do or say something racist (subjectively), you are racist. Your racism is confirmed by yadda yadda.
It's a pretty destructive tendency of people because it makes a lot of people scared to fucking death to talk about race at all. Even if you've got pretty liberal views on the subject in general it only takes one awful misstep for (certain) people to pounce on you and send you off to White Jail where you're served nothing but Budweiser and grits.
What I'm saying is twofold: first that I don't think that guy is wrong or evil just because one of his talking points happens to come off as hilariously backwards, and second that I had to check myself to make sure I'm not just saying "What a goddam hypocrite" and writing him off so that neither of us has a chance to actually learn something.