That would be unjust, because they have not committed any wrong, and the actual slaveholders are long ago dead.
And the descendants of slaveholders have had no wrong done to them. The actual slaves are long ago dead.
More money in the hands of taxpayers, any taxpayers, is a good thing. Less money in the hands of government bureaucrats is also a good thing.
Does the end always justify the means? Even at the expense of a vastly unjust tax system? So you would be in favor of abolishing income taxes on all Democrats? How about abolishing income taxes on males, people named Bruce, and people from New Hampshire? The real tax rate determined by the rate of government spending. Cutting taxes on a particular group only changes the tax allocation unless you cut spending as well. Even cutting taxes across the board changes the tax allocation from people living today to people living in sometime in the future if there are no corresponding spending cuts.
By the "logic" that's wafting up my tailpipe tonight, I'm "entitled" to own half of Egypt!