> A reparation is a material compensation for a past harm.
That's not correct. First definition on google: "the making of amends for a wrong one has done, by paying money to or otherwise helping those who have been wronged." Reparations are not limited to material compensation.
> You don't take away from a group, you take away from individuals.
A group is a collection of individuals. Some things happen on the individual level. Other aspects or dynamics are only present on the group level and must be analyzed there.
> But a position at a company is a limited resource. And if one person get's the position the other person can't get it. This is very much a zero sum situation.
This is correct on the specific dimension you are looking at. But you are ignoring second order effects. That job may have a significant positive effect for the marginalized individual, and then in turn have a positive ripple effect on the marginalized community that he or she comes from. This could certainly result in a positive sum situation for society as a whole.
EDIT: To be clear, I'm totally with you that this could be taken too far, and we must proceed with caution. I also agree we should try to focus on cases where the positive sum benefits are most clear. But it is a difficult problem, and I think many instances of positive sum benefits are not fully appreciated.