The great irony of our current religious moment is that the once marginal groups that flourished as a result of the original separation of church and state now hope to use their new influence in the federal government to take away the religious freedoms that made their rise possible. The United States inadvertently created a setting in which all sorts of views might thrive, a fact that allowed fundamentalists and other variations on Christianity to grow. Had the founders imposed a religious establishment, the groups that promote establishing religion today would have been on the outside looking in, persecuted and marginalized. Now adherents of these groups believe they have the power to instate religious tests, and they claim to be acting in the spirit of the founders. But what they would establish would never have become the official religion in the revolutionary era.
The United States was founded upholding the principle of separation of church and state. The first Amendment to the Constitution guaranteed religious liberty, that the government would make no religious choices for its citizens. At the time, numerous religious groups clamored for such an amendment, fearful that a stronger central government might dictate religious choices unlikely to square with their own preferences. The deep background they had in mind was Europe, where religious establishments were common and Christian religious minorities persecuted or banished. In their more immediate past, they knew that some colonial governments had treated certain Christians as second class residents. They wanted to avoid the violence and exclusion of Europe and the restrictions of colonial Massachusetts. They wanted to be left alone to develop their own faiths without interference.
This novel religious experiment in liberty had the effect of opening up new religious possibilities and allowing variety to take root. It was in the context of American religious freedom that Joseph Smith dug up ancient tablets and, using special glasses that allowed him to read those tablets, dictated the Book of Mormon. From his discovery Mormonism was founded, and the Church of the Latter Day Saints—despite vigorous and at times violent opposition—went on to become a major American denomination with a worldwide membership today. Only in America, as they say.
Similarly, evangelical Christianity—based on extemporaneous preaching and the idea that converts required an experience of being saved—flourished in this open environment. Preachers traveled by horseback to isolated rural and frontier communities, bringing their message to people who resided far from any organized religious institutions and seldom attended church services. Later, and largely within this evangelical community, religious fundamentalism—the idea that the Bible could be read literally and as if it were a straightforward and transparent text—eventually spread widely and gained many converts.
Had the United States started with an established church, it would have been neither Mormon nor fundamentalist. Both LDS and fundamentalism arose after the founding and so were not candidate to become the establish church. If the US could have agreed on an establishment (and founders knew that the attempt would threaten the unity of the barely United States), it would have been Episcopal, a newly-erected church structure based on the old Church of England. That church—headed by the English monarch—had been legally established in a number of colonies. Neither the Church of England prior to the Revolution, the Episcopal Church after, or any other single Christian church ever attracted a majority of Americans. Diversity compelled the founders searching for a basis for unity to advocate separation in the first place.
Although it was never established, the Episcopal Church did continue as the preferred faith of many American political and social leaders for a century and more after the Revolution. More than half of the first fifteen Presidents were Episcopalians. Yet today Episcopalians do not represent the establishment the Christian right envisions; they allow women to serve as clergy and offer broad acceptance of LGBTQ persons.
The great irony then: the freedom of the American religious environment, created by separation, allowed marginal religious options to flourish, and these groups now seek to end the separation that made their very existence possible. They want to force their religion on the rest of us. And they seek to do so claiming that they honor the intentions of the founders. It would be more accurate to see their rise as an unintended consequence of the freedom granted by the founders.