When the Constitution was written, much of it was debated until debate just wore out. They knew, at the very moment the Constitution was adopted that not only was it flawed, but that it could not and would not last forever. Not because the Constitution was no longer useful, but because the people in the country would change until they frankly didn't deserve the Constitution any longer.
John Adams put it this way: "The Constitution was written for a moral and religious people, it is wholly inadequate for the governing of any other."
We are no longer a moral and religious people. Now the Constitution is inadequate because we have failed in the ideals.
Benjamin Franklin explained himself better. In the debate as to whether or not the Constitution should even be adopted, Franklin put it this way in his address:
" Sir, I agree to this Constitution with all its faults, if they are such; because I think a general Government necessary for us, and there is no form of Government but what may be a blessing to the people if well administered, and believe farther that this is likely to be well administered for a course of years, and can only end in Despotism, as other forms have done before it, when the people shall become so corrupted as to need despotic Government, being incapable of any other."
Speech of Benjamin Franklin - The U.S. Constitution Online - USConstitution.net
We have reached that point where we, as a corrupted people, deserve only despotism being incapable of anything else.
If you are teaching the Constitution, it is a good thing to include the debate as to the adoption of the Constitution.
We could return to Constitutional principles and again become that moral and religious people that John Adams mentioned, or follow liberalism to despotism.