I want to ask you a question.. if an effective means or special technology was deviced to ensure that hacked accounts would be reversed, who would have the power to reverse the funds? A particular set of people or or every single person can have the power to reverse funds? If it's left in the hands of one person, then anybody would start reversing the funds of anybody they don't like, or even sell their coins to people and reverse it back when they have been paid, when it's left in the hands of a few people, it would be a centralised feature in a perfectly decentralised blockchain infrastructure and would put too much power in the hands of a few people.