If your member of an underrepresented group, chances are you didn't grow up to develop merit. Affirmative action allows you to access institutions that help you to develop merit.
If someone isn't of MIT-calibre merit (ie competence), then it's no good to them to pop them into an electrical engineering course that they can't handle, and it's especially no good for the ultra smart Asian American who was just racially discriminated against. They'll be better off at an easier institution where they'll have plenty of room to develop, and that unfairly excluded Asian will be better off at MIT.
