Third choice may be to just help an underprivileged class? Even non descendants of slaves have to go through the same BS as descendants of slaves for example. It's not about sticking it to racists, but about protecting a community.

Initially, I was just answering the question by playing devils' advocate but I've been drawn into this now.

It may be the case that someone will support quota systems' as a form of charity to a particular 'community' but people from other countries don't naturally become part of the same 'community' unless they're forced to be. It's only in the eyes of others that people with different backgrounds are lumped together, merely from having similar skin colors or accents.

For example, Latvians, Russians, and the British all share the same skin tone but it'd be a real stretch to say they're all part of a single unified community and they're at least all on the same continent. And even as immigrants they still retain a measure of pride, which brings me to my next point...

In my experience, you'd be hard pressed to get a Nigerian or Ghanian to admit that they're part of an underprivileged class. You'd have an even harder time getting them to say 'we are one people'; the rivalry between the two nations is very strong despite being two English speaking countries within a sea of Francophones.

Immigrants from those countries, at least, view themselves pretty highly which is born out in high-test scores, high incomes, and general life success. And although the children of some will integrate fully into the existing black US community, for the most part the older generation just views native African-Americans as foreigners.

It'd be better to support this on the grounds of diversity since then you can narrowly target smaller immigrant communities (e.g. Lesothans), or pick out particular groups for charitable aide (e.g. Rwandans)