By convenience sampling in my personal life and observing public figures, I see a certain proportion of successful folk are black.

Public figures are what, a few dozen at most? So you rely on your personal sample and why in the world do you think that it's representative?

Let's take our favourite people -- Alice and Bob. Alice lives in rural Alabama. She knows zero smart black people and extrapolates her personal sample to "all black folk are stupid". Bob hails from Idaho and is an undergrad at Harvard -- 100% of black people he knows are very smart. He extrapolates his personal sample to "all black people are smart". Why is your sample any better than Alice's or Bob's?