POS=no production cost=no value
If I can produce a coin without any cost, why should I pay any thing valuable to exchange it??? I will just go ahead to mine it
Fiat money can do this because there is a law to force its circulation, and the cost to make that law can be a war, which costs millions of times more energy than POW mining
https://bitcointalk.org/index.php?topic=848881.0Point 7
It is not labor theory of value, it is a simple fact that people will always select the lowest cost method to get a coin. POS miner can not get it since they think a POS coin could have same political position as fiat money, sadly no one listen to them because they don't have any army
And POS coin is against the nature of decentralized system: It is fixed by a small group of stake holders while the others can never change the system even if the time comes. The POW coins instead will change when the majority of hash power decided that a change is necessary