You do understand you will never convince miners to erase 3,000 blocks of the blockchain however if you did, then Bitcoin is done. Remember over those 3,000 blocks, newly mined coins have been involved in transactions and this action would double spend all of those. The coins originally minted would never exist and thus the coins spent wouldn't. Merchants, other users, exchanges would all see the downstream transactions (which have 6 ro 3,000+ confirmations) suddenly go unconfirmed and invalid.
While this in theory could be done at any time it is generally accepted to be impossible. If miners by decree can double spend transaction not 1 or 2 confirmations into the blockchain but 3,000 blocks deep then no receiver can ever be sure that the transaction is irreversible. There is a certain level of faith in all currencies that create the perception of value, and Bitcoin is no exception. Among those faiths, Bitcoin users believe that while it is possible in theory to 51% the network and undo transactions thousands of blocks deep, that it would have such an economic cost that it infeasible. All users accept this faith or they wouldn't be using bitcoin (or would require 10,000+ confirmations before concluding the transaction). Your proposed action (although I think it has no chance) if successful would break that faith. Without faith in the irreversibility of transactions, there is no value or utility to Bitcoin. Bitcoin would be dead. I am not talking the exchange rate goes down a bit and recovers, I mean completely abandoned as a worthless experiment and development moves on to future systems which don't have the vulnerability (likely some floating checkpoint system which acts as a check to the proof of work).
How do you use a currency that at any time could simply be "undone" and erased from your wallet by the actions of a third party? Would you use that currency? I know I wouldn't. I genuinely feel sorry for those who lost significant amounts of money by misplacing their trust in MtGox but this is a situation where the cure is worse than the disease.
Great post!
On the other hand it'd be great to have a way to "invalidate" the stolen coins, that would only affect the thief that could not spend the coins anymore...
All the other coins would increase in value, so that's good for the community as a whole, even if it does not repay the people whom the coins were stolen from.
This invalidation/block could be optional of course.
I think if something like this could work, it would also reduce the potential issues in the future.