Discrimination can be understood as “making judgment based on general, rather than case-specific, information”. For instance, racial discrimination is making judgments based on one’s race (general information) rather than one’s own merits (case-specific information).
However, people often find certain types of discrimination morally acceptable. For instance, it is usually okay for an employer to outright reject job applicants without college degrees even if it is possible that some without a degree are more qualified. People are often also okay with employers giving more consideration to those who went to better schools, even though some students from lower ranked schools can be better.
There are many such examples. Human beings cannot spend infinite time to acquire information in each task, so they use shortcuts which, usually, involve some kind of discrimination.
The question is: why do people find certain types of discrimination unacceptable but others acceptable?