Tradition and Originalism

I'm currently reading the opening passages of a dissent by Mr. Injustice Scalia from a case holding that nondenominational prayer at the beginning of a public high school's graduation ceremony was unconstitutional. Here are the passages that have got me thinking:

"In holding that the Establishment Clause prohibits invocations and benedictions at public-school graduation ceremonies, the Court--with nary a mention that it is doing so--lays waste a tradition that is as old as public-school graduation ceremonies themselves, and that is a component of an even more longstanding American tradition of nonsectarian prayer to God at public celebrations generally. ... Today's opinion shows more forcefully than volumes of argumentation why our Nation's protection, that fortress which is our Constitution, cannot possibly rest upon the changeable philosophical predilections of the Justices of this Court, but must have deep foundations in the historic practices of our people."

Notice something about this rhetoric? Not once does he mention the law. He does not even state that the Court is overturning legal precedents or traditions, merely that its current holding will destroy a cultural tradition. As best I can tell, the force of his legal argument, to the extent that he is making one in this passage, is that, well, we as a nation have always done X, therefore X must be constitutional. But there's a problem with that, isn't there? Isn't it possible that we were doing something for a very long time that was genuinely unconstitutional but which nobody noticed was unconstitutional? My professor in this course is Steve Calabresi, one of the founders of the Federalist Society, a former clerk of Scalia's, and a professed originalist. But he believes that originalism is not about insisting that any American tradition must be valid. Instead, Professor Calabresi argues, an originalist should admit that people can misinterpret their own rules. For instance, he says, his analysis of the historical record suggests that the Fourteenth Amendment's Equal Protection Clause was designed to prevent the creation of a caste system. That was the original intent. Now, very few of the legislators enacting that Amendment thought that the various differential treatments of women that were traditional in their society constituted a caste system. They were wrong about that. According to Professor Calabresi's philosophy of originalism, this means that the Equal Protection Clause does protect sex discrimination, even though its drafters most certainly thought it did not, because they misunderstood the fundamental principle they were enacting into law. (Incidentally, Justice Breyer's most recent book also argues for examining original intent at the level of underlying principles.) Applying this same idea to the case of invocations at public-school graduation, Scalia is perfectly within his rights to argue that the Court is overturning precedent, although I'm not sure there's any specific Supreme Court precedent for him to cite. But it's not enough to say that something is traditional to show that it is Constitutional. It's possible that the centuries of Americans holding invocations at their high school graduations were in fact violating the true, original meaning of the Establishment Clause all along, and they just didn't realize it.