Someone saying they won't serve a person or hire a person for a job because the person is gay is no different than doing it because they're black

I agree with you. However, that is not what Indiana's "Religious Freedom" law was all about. Many Christians (and I really wouldn't know about that personally since I am Jewish) believe that marriage is between a man and a woman because that is what their religion teaches them. The law doesn't that they do not have to serve a gay person who, say, walks into their restaurant. That behavior is still, by definition, discrimination. It does, however, protect them from having to actively participate (by having to cater) in a (religious) event that they believe is sinful.

You really shouldn't use such a broad brush...