There are different kinds of discrimination. Some one being completely out of shape for a job so they are unable to perform it is such an example. Such distinctions are acceptable to a meritocratic society. On the contrary, stating "You cannot do this job because you are Black", even though that person can clearly do the job in a professional manner is a discrimination which is clearly unacceptable. Now replace "black" with "male/female", "heterosexual/homosexual" and other such examples which do not affect that persons performance, then the same applies.