Religious freedom. Forcing someone to obey a law that's against their religion is a violation of civil liberties.
What happens if they change religions, or change interpretation of their existing religion and now support things they once opposed and oppose things they once supported. Can they now ignore different bits of the law depending on what they decide to believe in?
Why should religious freedom be the only 'freedom' that should be allowed to opt out of the law. What about non-religious positions? What about ethical stances? Political ones, ideological ones. If you are a self described fascist and the traditions and stances of fascism resonate with you in your daily life and give you order, purpose and morals, should you be allowed to opt out of the laws that go against your fascist beliefs?
What about the other parts of the First Amendment? If it's your Freedom of Speech to say you think the races shouldn't mix, should you be allowed to ignore a law that's against their personal beliefs? Should the press be allowed to ignore the law because their rights are protected?