That's at least possible, and I noted it at the outset. But forbidding members of the groups that are discriminated against to compete by offering to work for less deprives them of the ability to (a) compete by offering their services at a better price (b) that is more than they are making at their current crap jobs. It works to the advantage of the people who have skilled or otherwise desirable jobs at the expense of both the employers and the people who would like those jobs but can't get them because of discrimination.