Why is supermajority required for proposing a constitutional amendment

Because even though it is old the Constitution of the United States is the most well thought out document in history. The founders were even smart enough to put in a provision for it to be changed by Amending it. They were also smart enough to know that a mob often wants to change things with no regard to the unintended consequence. By requiring a supermajority, the founding fathers ensured that there would be a debate before any changes were made and that a supermajority would have to agree to the change.