Justice O'Connor, concurring in the case that struck down the Kentucky Ten Commandments display (paragraph breaks added, emphasis added), writes:

Reasonable minds can disagree about how to apply the Religion Clauses in a given case. But the goal of the Clauses is clear: to carry out the Founders' plan of preserving religious liberty to the fullest extent possible in a pluralistic society.

By enforcing the Clauses, we have kept religion a matter for the individual conscience, not for the prosecutor or bureaucrat. At a time when we see around the world the violent consequences of the assumption of religious authority by government, Americans may count themselves fortunate: Our regard for constitutional boundaries has protected us from similar travails, while allowing private religious exercise to flourish. The well-known statement that "[w]e are a religious people" has proved true. Americans attend their places of worship more often than do citizens of other developed nations, and describe religion as playing an especially important role in their lives. Those who would renegotiate the boundaries between church and state must therefore answer a difficult question: Why would we trade a system that has served us so well for one that has served others so poorly?

I'm sure this will be quoted often — but is it really apt? For much of our nation's history our system has been (by and large) little legal coercion of religious practice, coupled with routine government references to religion, including displays of Ten Commandments memorials; displays of creches; graduation prayers and even daily prayer in school; Presidential preclamations and Congressional acts praising religion; references to God on coinage, in the National Anthem and elsewhere, references that likely contained, at least at the time, some message of endorsement of theism; and more. And this has continued until recently: I suspect that standalone creches were quite common until the 1989 decision striking them down, graduation prayer was quite common until the 1992 decision striking it down, and Ten Commandments displays, even ones that the Court would now consider unconstitutional, were fairly common until today.

What's more, little legal coercion of religious practice, coupled with routine government references to religion is the system that Chief Justice Rehnquist and Justices Scalia, Kennedy, and Thomas would adopt. Justice O'Connor's system is much less tried and true.

Now Justice O'Connor might well be right on her bottom line: Perhaps barring Ten Commandments displays, and similar government endorsement of religion, would further strengthen American traditions of religious tolerance, and would increase the religiosity of Americans to boot. (Query why increasing the religiosity of Americans should be any concern of the Court's; perhaps as to that, she meant to ask why supporters of religion should want to trade away a system that has served them so well.)

But it seems to me far from clear that her argument for that bottom line works here. That a routine-endorsement-of-religion system has done good things in the past (compared to systems whose flaws went far beyond endorsement of religion) doesn't mean that a no-routine-endorsement-of-religion system would yield equally good results in the future.