The U.S. Constitution is the oldest serving founding document, and as such documents go, it's on the short side. It has been amended only twenty-seven times in its almost two hundred twenty year history. As much as the members of the Constitutional Convention seemed to have intentionally made it a flexible document, do we seriously think the constitution of an agrarian preindustrial society of 4 million? By comparison, that's the same population as the modern Central African Republic, with just over half its population density.
No constitution on this planet approaches the sacred text status that the American one does. I share that feeling of reverence. It's a document that was ahead of its time and a testament to the Enlightenment, but by no means perfect or universal. I've found myself wondering if among its strengths, its greatest - its continuity - is an extrinsic one, supported by a dedicated body of legal scholars in the form of the Supreme Court interpreting it in ways that (usually) adhere to the tastes of the people living at the time of the decisions. If that's really all that's going on, there's still something to be said for the sense of stability provided by a continuous constitution, and at least forcing a legal body to find contortions that allow us to continue considering that constitution as remaining in effect. But still, at the risk of revealing an unsophisticated understanding of jurisprudence, if the Constitution is the basis of the rule of law, isn't such a practice legal heresy?
There were some basic value differences between most modern Americans and the men who wrote the Constitution - for example, the expansion of the voting franchise to women, non-landholders, and non-whites. The right to vote has been expanded based on amendments to the Constitution, which is how it's supposed to work - but isn't it safe to conclude that there are other values embedded in the document intentionally by its creators which would now be anathema to us? We can't ask Madison directly whether there are any unanticipated horrifying interpretations of the document of which he was, if not the father, at least the mid-husband; but there are several ways to objectively ask whether constitutional law is really just about interpreting a written constitution in whatever ways best satisfy current public taste. A beginning would be to see if similar legal questions have reached the Supreme Court more than once, and then tallying whether the outcome of those cases has changed consistently over time. For me, the best answer would be a "no" that allays my suspicions. I'd rather a civilization be based on foresight and reason, rather than legal contortions to preserve the illusion of continuity - but I'd also like to be able to tell the difference.