"...every person has the right to choose his own religion. But this right must be predicated on the basis that everyone has the right to his own private religion."
This seems to be the case: I, for example, have recently moved from an indifferent agnosticism to a slightly less indifferent deism. As I live in America: there's no formal religious test applied to me (or anyone). Bluntly: nobody give a fig what I do or don't believe or how my views have shifted.
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"...in choosing a religion that is corporate, as with most religion today, in its powerful sects and churches, once any great part of the population chooses the same religious sect, its corporate power is unleashed. And before long all of a given society and country may be under its thrall."
Depends on the society: In America there are a great many kinds of religion practiced. Sometimes adherents of this one or that one attempt to 'legislate' their religion (just as areligious folks sometimes attempt to 'legislate' against religious practice). American government unevenly safeguards against such by way of the 1st Amendment. There are abuses and oversights, sure, but mostly the individual is free to practice a religion alone or corporately and prohibited from forcing others to do the same.
Now what happens in theocracies is another matter entirely...