The argument for it at the Supreme Court was basically cold hard math.
California banned it in the late 90’s, which basically gave the US a massive control variable. In the data set with AA, white and Asian students didn’t really have their futures and earning potential impacted by AA. That said, black and Hispanic kids saw massive lifts.
The other argument it is that the race neutral alternatives that were tried in CA over the last 25 years have not been as impactful at lifting the earning potential of black and Hispanic kids.