[treis]

They will know the applicant's race & religion within the classification system the employer uses. In other words, in the eyes of this hypothetical employer the racial system is Black & Not Black. By not checking the box they know for certain that the employee is Not Black and presumably eligible to be hired. The fact that others might subdivide Black or Not Black into different categories doesn't change anything for the employer.

[notahacker]

Sure, but the 'homosexual/heterosexual' classification system the other hypothetical employer uses is also intended to ensure that women are ineligible to be hired if they have the same sexual preferences as those men who are eligible to be hired, and vice versa. One could argue that this treats men and women 'separately, but equally' as both have the chance to be hired under different hiring criteria unlike the illustrative example, but 'separate but equal' is so well understood to be unconstitutional it's not really worth raising as a counterargument.