Diversity of confession and denomination characterize US religious history. In most of US history God's would-be publicists who found themselves thoroughly without reserve convinced of their special closeness of to God or Jesus would be perceived immediately as a threat by all the other denominations. To paraphrase one summation of Federalist Number 10: the cure for the domination of religion over public life is to have more religion. More sects result in more opportunities for avoiding the domination of any one sect. The cure for faction is more faction, religious or otherwise.
The absence of religion in American Public Life much decried by religious types is not the result of a secular conspiracy. In an time when members of a church or synagogue took the differences between the various denominations far more seriously than is hardly conceivable today, religion couldn't be established by political bodies, nor could it be legislated against by political bodies. Considered in this way, the Establishment & Free Exercise Clauses largely amount to the same thing. If one denomination were given the imprimatur of Congress, then it would be an attack on the Free Exercise of religious practice by all those other denominations that were excluded.
In this context, the homogenization of American religious life that Evangelical Christianity represents threatens freedom and liberty. American Evangelical Christianity is primarily a political ideology not unlike Bolshevism in so far as its primary concern is effecting change in this life, in this world.