I can't tell if you are being willfully ignorant, or the other kind. I'll say it again--UNC justified its policy solely on the ground of the asserted educational benefits of diversity. You and others (including Trimp) are making a reparations-type of argument. You can argue that until you are powder blue in the face, but that is not part of the case.
If you are defending UNC, you have to show that: (1) the putative justification for the policy--the educational benefit of a diverse college education experience--is a compelling governmental interest, likely by (a) assuming that White and non-White college students are so different from one other that there is some associational benefit to having them sit together in class and (b) measuring the benefits of the policy in terms of the benefit for White students of having more non-White students around; and (2) the policy is narrowly tailored to serve that interest such that it is the least restrictive means of doing so--i.e., there isn't any other race-neutral way that the governmental interest could be served, such as admitting the top 10% of every NC high school's graduating class, basing admissions decisions on socio-economic factors, etc., etc., etc.
That's the framework this will analyzed under. Best of luck.