Will you inherit the monies your parents paid into Social Security if your parents never lived long enough to collect what they paid into that fund? Why not? That was money earned by your parents and contributed to a fund intended for their "retirement". Why should the descendants of those contributors not inherit the money left unpaid?
False equivalence. SS by definition is not the same thing as money invested and used to assist your specific dependants. SS is a required tax. If it was up to me it would be given to the descendants..
Although billed as a tax, it is a forced contribution to a retirement fund administered by government. If you had the choice of contributing to a private fund, any money held on account at your death would accrue to your estate. So, yes, I suppose it is somewhat different because a definite amount of money has been contributed and will never be distributed to the heirs of the deceased. Hence, the government has stolen some amount of money from the citizens.
Reparations for descendants of slaves features no specific fund designated for that dispersal. So, you have no fund designated for that purpose. Your solution is to force all current taxpayers to make some contrition to your fund. OK, you have identified a source for your reparations. The question remains: who should receive reparations and how much? What data do you propose to use to calculate the amount to be dispersed?