"so that marginal black people could have those positions." In the first half of the 1900s, it was legal for government-funded schools to deny academic positions to qualified students based on race. Until the 1990s, it was legal for private institutions to bar students based on race.

Affirmative action isn't about giving up the bottom 10% to unqualified minorities. It's about giving qualified candidates an opportunity they would otherwise have been denied. If the institution chooses to waste those spots on unqualified minority applicants, it's the fault of the institution and not affirmative action in general.

BTW, you appear to be conflating welfare with affirmative action in #1, 2, and 3. They aren't even remotely the same thing.