Ah, okay, I think I understand what's going on here. The post seems to imply that all white people go around selectively quoting MLK, which feels unfair.
I too am white, in case you hadn't already inferred that from my profile. I'm not offended by the quote, partly because I never quote MLK, so I know that OP is not referring to me. But also because I understand that the construction "White people do so and so" is not used to mean "all white people do this all the time", but is rather a way of drawing attention to a commonplace behaviour among white people that the speaker finds problematic. So when I hear it, I use that as my cue to reflect on whether I myself ever do that thing, and the impact that my behaviour might have on other people.
The construction seems jarring at first because it offends our expectation that we be treated as an individual, and be given due credit for our good behaviours. The irony is that we only have that expectation because we are white. People of colour have spent their whole lives being treated by society primarily as members of their group.