This has been proposed before in other situations. For example, the Mt. Gox coins were proposed to either be "destroyed" or sent back to their purchasers with

This has been proposed before in other situations. For example, the Mt. Gox coins were proposed to either be "destroyed" or sent back to their purchasers with a blockchain update. This introduces serious problems with the question of "who is everyone" (when you say, agreed upon by everyone). In other words, is the community going to set up a centralized board to hear complaints and reverse transactions? Does this turn into "I bought a trinket on ebay and the guy didn't send me the thing, reverse the transaction"? Part of the strength of bitcoin is a permanent historical record. There's been some suggestion that the true long-term benefit of bitcoin is not in the "money" part, but the blockchain itself. As soon as the blockchain becomes mutable, then this value becomes suspect, and the line for "how bad does it have to be before we edit the blockchain" might get weaker and weaker.