A better argument would be to point toward proof of stake or other consensus systems like that used in Ripple. Until there is a more effective method, Proof of

A better argument would be to point toward proof of stake or other consensus systems like that used in Ripple. Until there is a more effective method, Proof of work is a highly effective alternative to physical security. Trying to pass off counterfeit government currency has consequences that involve work by numerous individuals and organizations - and they don't always succeed. Proof of work in a crypto system is effectively successful all of the time, instantly. The same applies to any form of money and fraudulent activity since the beginning of history. There is always work involved, and the effectiveness of that work has never been greater than with crypto... the consequences of which must be kept in mind - just like existing governments and systems, crypto can be used to control its participants.