When government starts protecting a class like race, gender, religion, or sexual orientation, but not protecting those whose views may be offensive to those classes, the government is picking winners. Beliefs are as fundamental to who you are as are the other protected classes. Someone can no easier be "not gay" than someone else can "not believe that gay is abnormal". The difference is protected classes don't have to hide, but people with unpopular beliefs do, and that's not fair.
When we protect age, gender, race, ethnicity, religion, and sometimes sexual orientation and gender identity why not political affiliation and beliefs? Employers should not be allowed to fire their employees because they are in the "wrong" political party. Nor should people get fired for airing a controversial political opinion around the water cooler.
No, political affiliation and beliefs should not be protected from discrimination, because people should have a right to associate with whom they want to. It would be unfortunate if someone couldn't send a message by refusing service to a person with beliefs with whom they disagree with. It is also hard to provide someone good service if you have a fundamental disagreement with them.