We don’t have freedom of religion in this country.
We can’t. Not “we don’t want to”, not “we shouldn’t”; can’t, as in “it’s impossible”. Not even antigravity impossible, either — current science says antigravity is impossible, but if scientists discovered something new it would be possible without contradiction. We’re talking “red and blue at the same time” impossible, a direct binary logical contradiction between mutual exclusives.
“Exclusive” is the key concept. Religions worthy of the sobriquet are exclusivist, declaring that theirs is the One True Way and all others are somehow defective. This is almost, but not quite, always accompanied by a duty to go forth and teach the nations, bringing everybody to the One True Way. So far, so good. Each cat his own rat, and evangelizers are trying to do their targets a favor by helping them Get Right With God (however that particular religion envisions $DEITY). Evangelists may be annoying, but we don’t execute people for cutting us off on the freeway or laboriously counting change in the checkout line, either.
The trouble comes with religious practices. Every religion has God-commanded things adherents must do in order to remain within the religion, and some of those range from vastly annoying to destructive of societal cohesion. Islam, for instance, requires killing non-Islamics if they can’t be convinced to convert, and it isn’t the only religion that requires that. Baptists and Buddhists (among others) have to be alive to practice their faiths; if Muslims have freedom of religion, including killing infidels, the Baptists and Buddhists do not have such freedom. The contradiction cannot be resolved. If one group has freedom of religion, including religious practices, the others cannot.
There are lesser conflicts. Our society frowns on murder. There is more than one religion that either allows or demands sacrifice, including human sacrifice; by the tenets of the religion a human sacrifice is not “murder” but a sacrament; to the rest of us it’s unjustifiable killing. Again, the contradiction cannot be resolved because we have a mutually exclusive set of requirements.
What we do have in the United States and most of the West is religious tolerance. Private worship is just that, private, and nobody’s business but the worshipper’s; practices that don’t deviate too far from the societal norm are allowed, though they may be disapproved; practices that deviate beyond those bounds are forbidden on a secular basis. Adherents of some religions are forbidden to engage in some of the practices required by their faith, and thus do not enjoy full religious freedom.
But what sets the norms?
Religious practices, like most things, are created by evolution. Societies evolve just as species do. Practices arise within a society. Those practices either promote the success of the society, are neutral in their effect, or are damaging to societal success. Societies that adopt damaging practices fail to survive and perpetuate themselves, and so fall out of History, leaving few if any traces. Societies that adopt success-promoting practices survive, grow, and perpetuate themselves.
The phrase “survival of the fittest” is pithy, apt, and wrong. What evolution guarantees is survival of the fit enough in the context in which the species or society exists. All of the societies we encounter today have passed this test — the practices they have adopted are sufficiently productive of success that they are fit enough to have survived the tens or hundreds of millenia since human societies have existed.
None of the members of a society have, or can have, any clue as to where their practices came from. They arose spontaneously and at random; perhaps one of the members of the society, long ago, had a brainstorm or a bad dream, leading him or her to do something new. That new practice spread to the rest of the society and contributed to its success (as we know, because the society has survived), but its originator is long forgotten in the mists of ailing memory. Lacking any knowledge of where the practices came from, the members of the society attribute them to God as Commandments. Religions have each their own set of societal practices, codified as the Orders of God because their source is evolutionary and therefore not evident.
There are several such sets of practices — religions — in existence today, all of them successful in terms of survival of the fit enough. One of them is Islam (“successful” is not synonymous with “nice”). Another is often simply termed “Christianity”, although it is a complex mélange of Judaism, founding Christianity, and Roman practice as modified by the historical Church and the so-called Enlightenment. Judæo-Christianity (for short) is currently far and away the best promoter on the planet of societies which feed their children and produce wealth and comfort in their members (although Buddhism comes close).
The United States is not “a Christian Nation”, but its Founders and the Framers of the Constitution were firmly embedded in the Judæo-Christian belief system. Some of the Founders were Believers, and some were not, at least as understood in modern terms. “Deism” is properly a specific religion with its own set of imperatives, but it does include acceptance of a set of practices as leading to success whether or not attributed to $DEITY, so it makes a reasonable catchall for the attitudes of the Founders, whether or not any of them would have described themselves as Deists — and it sits well within the Judæo-Christian tradition.
One of the significant components of Judæo-Christianism is the matter of sacrifice. It would be possible, with some work, to dig through the Pentatuch and derive a fundamentalist version of Judaism which permits or even requires human sacrifice, but Judaic tradition does not support such a thing (or even animal sacrifice) in its current incarnation(s), and in fact no such sect currently exists. The Christian tradition has no need for human sacrifice because sacrificing the Son of God suffices once and for all, and rejects animal sacrifice for many of the same reasons Jews do. This, alone, would go a long way toward serving as the basis for a cohesive society, and there are many other Judæo-Christian Commandments that are also supportive of societal success; “Vengeance is mine, saith the Lord” is somewhere near the top of that list.
Those are the norms. Religious practices which fall within the (rather broad) limits of the Judæo-Christian ethos are freely permitted; those which do not are deprecated or forbidden, and adherents of religions which require them do not have religious freedom. Atheism falls snugly under that umbrella — yes, atheism is a religion; nothing makes that more evident than evangelical atheists’ hysterical and forceful attempts to suppress visible religious practices, or, rather, visible other religious practices — so long as the atheists accept the practices as societal norms. That’s how the Founders saw it; when they spoke about “religious freedom” they meant freedom within the Judæo-Christian ethos, and they were dismissive (sometimes sneeringly so) of religions that did not fall within those limits. The structure they built was much more elastic than they themselves imagined, and today we can accommodate a much wider variety of faiths than they contemplated — but practices that are endemic to non-Judæo-Christian religions and contradict the Judæo-Christian ethos are not, and cannot be, accommodated. Attempts to do so are self-contradictory and destructive.
 Buddhism, which has a Prophet but no Deity, is treated as a religion in Law. Close enough for Government work is exactly right.
 Compare and contrast the Anthropic Principle, as discussed previously.