It also screws up the earnest ones who struggle in colleges above their preparation level, shall we say—and give up being the perfectly fine, mediocre whatever they would have become at a less competitive school.
For years UC Berkley accepted affirmative action students with low SAT scores. Their graduation rate was very low. When they changed their admissions standards and only accepted students with better scores the graduation rate greatly improved.
Liberal do-gooders actually hurt the AA admits. They throw these poorly prepared students into classes where they have no chance to succeed. They flunk out and return home as losers. Had they gone to a less selective school they might have done very well.