Well, let's just take one example, shall we? One example of many.

For decades, the federal government discriminated against blacks in home loan lending practices, while massively favoring whites. This occurred mostly from ~1930-1970. The result was that many tens of millions of whites became homeowners, and went on to become moderately wealthy by virtue of that. Home ownership is (or at least was, during that era) a great way to build family net worth. The white middle class as it came to be, post-war, was thus in large part a product of these government programs. Meanwhile, the blacks were shut out. And the result of that was that black family net worth stagnated -- and that from a very low bar. We see the results today in the dramatic disparity of white versus black family net worth. This is largely the result of the institutional racism of the U.S. government in decades past. Note that I said LARGELY the result; not entirely. Of course there were other factors. But that was the big kahuna.

SO, what are we to do to rectify this? Nothing? Just say to the blacks: "stop complaining and work harder"? Would rectifying this historic crime be giving a "free ride" to blacks "on the backs of hard working tax payers"? The whites who were given the enormously-favorable home loans are the ones who got the free ride, effectively on the backs of blacks. If that is not a "legitimate complaint", then what the hell is?

Background read if you are interested:
[link to www.washingtonpost.com (secure)]

And btw this is, as I said above, just one example of many. Anyone who chooses to sincerely study the issue of race in America will easily find many more.