Discrimination wrongfully imposes relative disadvantages or deprivations on persons based on their membership in some salient social group. But which salient groups count for the purpose of determining whether an act is an act of discrimination? This question is at the heart of many heated political and legal disputes, such as the controversy over gay marriage [not intended to marginalize the extreme racial discrimination that has occurred over centuries in this country].
The concept of discrimination picks out a kind of moral wrong that is a function of the salient social group membership of the person wronged: persons are treated as though they had diminished or degraded moral status on account of their group membership, or they are, because of their group membership and the relative disadvantages that they suffer due to that membership, made vulnerable to domination and oppression. But why have such a concept? Why not simply have the concepts of domination, oppression, and degrading treatment, abstracting from whether or not the reasons for such wrongs involve group membership?
Judgments about discrimination can and do reveal genuine wrongs that persons suffer due to their salient group membership and expose actual patterns of disadvantage and deprivation that amount to systemic injustices against the members of certain salient groups. It is not necessary to take account of everything relevant to a phenomenon in order to understand and represent important aspects of it.
The concept of discrimination provides an explicit way of thinking about a certain kind of wrong that can be found in virtually every society and era. The wrong involves a group-based structure that works in combination with relative deprivations built around the structure. The deprivations are wrongful because they treat persons as having a degraded moral status, but also because the deprivations tend to make members of the group in question vulnerable to domination and oppression at the hands of those who occupy positions of relative advantage.
We should never treat others as having "degraded moral status." It is shameful that people can take such a position and look down upon another because of their skin color, gender, sexual orientation, ethnicity, age, religion, or disability.