For each block Dr Evil can add his evil transaction (illegally transfer ownership of an extinct volcano to Evil Corp).<p>If such a transaction is worth more than the cost of renting half the worlds commuters for ten mins then it&#x27;s worth doing to him<p>As such, we must make sure good actors are more incetivsed to hold 50% of compute power.  So the cost of renting the 50% must be 25bc or it must be socialised as the cost of not letting Dr Evil succeed.<p>If it is socialised, we would be insane to write a blank computing cheque for the future<p>So we may well want to have private chains with clear mechanisms for saying what is and is not allowed onto the chain.<p>Blockchain is a bit socialist right now - anyone can add any transaction.<p>I cannot imagine it surviving like that - but then the Internet is not doing too badly against the same forces - the compromise may be progress