Being in a legally protected class protects you from discrimination on the basis of membership in that class, it's still legal to discriminate against you for any other reason.

For example: I cannot refuse to rent a house to a person because they are black, but I could refuse to rent to them because they are a democrat, or work for Microsoft, or drive a Ford, or any other reason that isn't age, race, gender, etc. If they happen to also be black, it doesn't matter.