Why is the right of freedom of religion an important right for all citizens?

Freedom of religion is important in a democratic and pluralistic society as another way of protecting minorities from the "tyranny of the majority". All the Rights in the Bill of Rights are meant to protect the individual in their own "pursuit of happiness" in America for example, and the right to believe or think for oneself is part of that. Many nations at the time of the American Revolution had "state religions" supported by the government, such as the Church of England (The Anglican Church), which was and is currently headed by the King or Queen of England. Other nations, like France, adhered to Catholicism with the Pope of Rome as its spiritual leader. Many smaller, Christian sects, were persecuted by these state religions at the time.

During such persecutions, for another example, the era of The Spanish Inquisition, tortured and killed thousands, and over time, the persecution of religions not sanctioned by the state killed millions. As well, throughout history wars of religion like the Crusades, or correspondingly, Jihads in the Middle and Near East, were and continue to be especially brutal and without rules to treat civilians, as believers of a different religion were and are viewed as a lesser humans, or one who would lead others to some form of hell. As well, religion has been used many times to instigate wars or persecute minorities that were simply of a different ethnicity or class of people for the sake of political or financial gain.

The freedom of religion helps to provide tolerance for others within a nation and even internationally who believe in a higher power, whether of the majority of a nation or region or in the minority, or even individually. It guarantees a sort of marketplace of ideas and faiths to compete with one's mind or soul without fear of physical, emotional or financial harm. It also guarantees the individual the right not to believe in anything relative to a higher power or afterlife. It is part of the list of Human Rights that support the individual's right to pursue happiness.