>>54742115line of causation runs the other way chap.
SES isn't causal in determining IQ, we know this because shared environment has 0 effect on adult IQ scores. Shared environment is everything you'd share with a sibling growing up in the same home; nutrition, schooling, parenting etc. Doesn't impact it whatsoever, variance in IQ to some extent causes variance in SES.
Regression to the mean happens, but it is to the family mean not the ethnic one, that said Ethnic groups can be seen as big families if you look far enough back in ancestry so it's still useful to look at.
There's nothing wrong with 130 IQ black people, they're just rarer than 130 IQ white people. Regression hits blacks harder on average because it's less likely that the underlying familial IQ is representative (non-shared environment, which could really be anything that isn't genes or shared env impacts adult IQ, luck plays a role).
Also Putnam found in the US that social capital decreases as diversity increases, there's a decent, if vague, finding of the summary on this wiki page. Putnam is a liberal harvard prof btw, absolutely hated his findings and he sat on the paper for 6 years before writing a section pleading with people to ignore the downsides and go full steam ahead with diversity anyway.
https://en.wikipedia.org/wiki/Robert_D._Putnam#Diversity_and_trust_within_communities 
