What do you mean by a "serious diversity problem"? Not white enough, or what?
Just because we have a black female mayor does not mean the real racism of SF is gone, just as electing Obama did not miraculously cure the US if it’s racism.
I don't agree that they have been "ethnically cleansed." I'm sure economics has forced some out.
I've live in many parts of the country, and this is by far the least racist, and most racially diverse, place I've lived.
Black men in the city would be expected to have a lower life span than black men nationwide, since urban black neighborhood are more prone to drugs and gangs. Have you compared to other big cities, as opposed to just nationwide?
San Francisco also has a disproportionately low amount of black folks living there.