Wrong. It is your interpretation that this is an irreplaceable key. You are trying to say that a design is wrong, because you believe that your implementation would be wrong.

Uniqueness is a different property from replaceability. And, replaceability is not necessarily the correct property to design for, key rotation and recovery from loss are the properties. What you want is the ability to rotate keys and recover from the loss of keys.

The moment you ask users to manage keys, you've lost. They can barely handle passwords that aren't abcabcabc.