Let's say you live in a small town. This town has 4 gas stations. You're dark skinned, kind of middle eastern looking. All 4 of these gas stations refuse service to you because you might be a muslim and they don't like that. Guess you don't get a car. So take a bus. Woops, all the buses don't want any of your kind on them. Guess you walk. Well then some guys mug you because you look foreign. The cops don't care, you're brown and probably muslim. None of these businesses or services have to do anything, because there's no laws protecting you.
This is why these laws exist and are needed because that's a very real situation that our country battled with, except with race instead of religion, not even 100 years ago.
And no, this doesn't work both ways. There's a fundamental difference between disagreeing with someone's opinion and disagreeing with something about them they cannot change. One is just disagreeing, the other is discrimination.