You are correct, the Constitution as written by the Founders was for people who were generally moral and just, to allow the Constitution to be fiddled with by people today who generally are not moral and just is simply lunacy.
I don’t believe the states would send lunatics to the CC. Additionally I believe any foolish amendment would be voted down handily. I believe your fear, while on the surface reasonable, is not well founded. Beyond that, there is no other choice.