relationship status
relationship status is a ligitamate way to "Disriminate" as in differentiate, between people. just as it it perfectly legitamate to hire one person because hes smarter than the rest of the aplicants, its perfecly legitimate to give a married coupel extra rights because they are married.
and by the way, a single man is not equal to a married couple, the legal concept of marrige is supposed to make it easyr to allow one of the parents to stay at home while allowing them to take care of the kids.