Segregation was a form of affirmative action. The intent of the policy was to have good quality blacks ruling over ordinary blacks, analogous to the caliphate policy for dealing with ethnic diversity.

For which they needed black lawyers, black judges, black businessmen, etc – who needed, and received, protection from white competition.
Segregation manufactured a black middle class to govern ordinary blacks, a middle class that had real work to do, unlike the soul destroying makework done by today’s black middle class.