However, only the most naive would refuse to recognize that stereotypes exist, whether or not one believes them or does anything based on them.
Also, race, ethnicity, and somewhat religion are features that one tends to be born and raised into (and not easily changed), while joining a fraternity is a purely voluntary action taken after one reaches legal adulthood (like, for example, shopping or working at WalMart), so that the comparison is not really the same.