A very oversimplified pro argument: if it wasn't for slavery, these families would have generational wealth and better social situations. African Americans in the US ARE disproportionately lower wealth/income and this has CLEAR historical origins.
The oversimplified con argument: Okay, but if you come from a wealthy African American family, why should you have a leg up over a poor (or otherwise more disadvantaged) white student? What about an immigrant, who didn't benefit from slavery at all?
Fundamentally there's a huge swath of different injustices across society, and we obviously can't fix all of them at once, so a big challenge in this sort of debate is how you slice the injustices and how you prioritize fixing them.