Here is how I interpreted it.

He isn't saying to just ignore racism. What he's saying is to not let the rhetoric ("what have white people ever done for us") get ahead of reality ("white people have contributed to society in many ways, which we take for granted").

It's easy to lose perspective, but today's black and white Americans have more in common than black Americans and Africans. And while it's easy to get hung up on our differences, we share far more similarities.

So while racism and injustice should be addressed where it exists, let's not allow it to blind ourselves or perpetuate a false narrative. He distilled this idea down to a simple illustration, highlighting his point and exposing the rhetoric for its absurdity. Hence the "joke".

At least that was my interpretation.