[astrange]

Nothing is ever irreversible, it's just a question of how expensive it is to make the database writes. Ethereum forked the whole currency to undo a write (the DAO hack) and if the legal system can find a hacker they can make them reverse their transaction.

…But having someone with admin access over the network and can fix mistakes is just a lot cheaper than refusing to build that in for ideological reasons.

[JohnFen]

Most (but not all) things in life are technically reversible. But some things are so difficult or expensive to reverse that they are effectively irreversible nonetheless.