Why is Affirmative Action so Controversial and Do We Still Need It?

Affirmative action in college admission seems like an un-American idea. Why should one group or class of applicants be treated differently than others? Originally seen as a corrective to better balance historic prejudice against black applicants, affirmative action is considered “positive discrimination”. But, this is a controversial take. What does affirmative action mean today, and do we still
need it?