If I understand history correctly, it seems that American Christians at the end of the 18th century were much more sectarian than they are now. That is, they identified rather strongly with their particular denominations and largely rejected ecumenism. They wanted the government to sanction their own denomination and opposed the government sanctioning others. I imagine that most citizens probably didn’t think the Establishment Clause would entail total neutrality, and if the federal government wouldn’t make their own church the official national church, then they were satisfied that at least no other church received this status. And since almost all states had official churches at this time, there was no need for a national church.
American Christians today are rather different. Many of them change denominations, especially within Protestantism but also to and from Catholicism, some identify as “non-denominational,” and they all generally identify much less than with their individual churches than their ancestors did. Far fewer of them have negative opinions of other denominations or even non-Christian religions, with some even having favorable opinions of all other religions, especially when contrasted with atheism. This last sentiment is sometimes expressed as, “I don’t care where you worship, as long as you go somewhere.” While this may be relatively open-minded, it’s especially dangerous for church-state separation. Another problem is that historically disfavored minority denominations such as the Baptists have almost totally forgotten their former commitment to secular government now that the threat of another denomination becoming established has long disappeared and they have become a major group themselves, especially here in the southeast.
If the Establishment Clause, with its long history and secure position—requiring a constitutional amendment to repeal—didn’t already exist, I think a law establishing general Christianity as the official national religion would be a real possibility. At the very least, it seems that most Americans would not oppose a law which allowed government to favor religion in general, as long as it didn’t discriminate between faiths. I believe the existence of faith-based initiatives for over a decade supports this view. The average American thinks religion is good and doesn’t necessarily object to the government actively promoting it as a whole. I find this disturbing.
In the absence of a constitutional amendment, major changes to the law can still come through the Supreme Court. I fear a majority of the justices will eventually agree with the popular sentiment and simply overturn the precedent requiring neutrality toward religion altogether. It’s worrisome, but all I can do is vote for presidential candidates who are less likely to appoint theocrats to the federal bench and to support organizations that promote secular government. I suggest we all do the same in order to hold up the wall of separation between church and state.