Ilya Somin has an interesting post defending majority atheist societies. He writes:
There are numerous majority-atheist nations that show no signs of falling prey to communism or other similar ideologies. Consider the cases of Japan, the Czech Republic, and Denmark, among others - in all of which atheists are the majority of the population (for detailed stats, see here).
Indeed, those "atheistic" and more secular societies in Japan and Western Europe have fewer social problems than the US. And in the US, atheists, as a group, have more positive social indicators -- less likely to commit crimes, go to prison, or be poor.
Atheists' better social indicators, though, may not be a consequence of atheism; but rather both the atheism and positive social indicators may result from the same underlying cause -- well-educated, brighter people are both more likely to be atheists and less likely to commit crimes or be poor.
Indeed, I wonder if, like controlled socialism, atheism works well only among small homogeneous groups. I don't think if America became majority atheist, society would improve; indeed, we'd probably get a lot less interesting.
Though I am not a "multiculturalist," I think, after our Founders, that religious factionalism can be a socially positive thing -- so long as those factions are properly balanced in the right way with the right set of laws guaranteeing equal rights for all. More importantly, all factions ultimately must conform to the tenets of liberal democracy.
I like a society with atheists, agnostics, liberal Christians, traditional Christians, Catholics, Protestants, Jews, Muslims, Buddhists, Hindus, Wiccans, etc., all of them respecting liberal democratic norms.
If any social group doesn't respect the over arching principles of liberal democracy -- i.e., the Declaration of Independence -- then multiculturalism or multireligionism could be quite harmful.
As the Founders believed, "out of many, one" -- the right way to do pluralism. On religious matters, they didn't just embrace pluralism, but the key Founders thought nearly all world religions (including many non-biblical ones) were valid ways to God. Indeed, sometimes they oddly intimated that polytheistic religions worshipped the same one God -- Nature's God -- they worshipped. For instance, John Adams wrote the following to Jefferson, Oct. 4, 1813:
[BTW: Could someone check my Greek. I did the best I could with it. If anyone owns the Cappon ed. of the Jefferson-Adams Letters, it's on pp. 380-82.]
θέμίς was the Goddess of honesty, Justice, Decency, and right; the Wife of Jove, another name for Juno. She presided over all oracles, deliberations and Counsells. She commanded all Mortals to pray to Jupiter, for all lawful Benefits and Blessings.
Now, is not this, (so far forth) the Essence of Christian devotion? Is not this Christian Piety? Is it not an Acknonowledgement [sic] of the existence of a Supream Being? of his universal Providence? of a righteous Administration of the Government of the Universe? And what can Jews, Christians, or Mahometans do more?
Moses says, Genesis. I. 27. ["]God created man in his own image.” What then is the difference between Cleanthes and Moses? Are not the Being and Attributes of the Supream Being: The Resemblance, the Image the Shadow of God in the Intelligence, and the moral qualities of Man, and the Lawfulness and duty of Prayer, as clear[l]y asserted by Cleanthes as by Moses? And did not the Chaldeans, the Egyptians the Persians the Indians, the Chinese, believe all this, as well as the Jews and Greeks?…I believe Cleanthes to be as good a Christian as Priestley.
[For more of Adams' thoughts like this see the following.]
Joseph Priestly was, by the way, Jefferson's and Adams' spiritual mentor. Calling someone "as good a Christian as Priestley," is probably as high a complement you can get from Adams on religion.