In my original post I give an example of why that's not true. The same guy can own all the big PoW hashing pools in secrecy, which is a sybil attack, not collusion. He can operate profitably the entire time and initiate the long con or other strategy whenever he wants.
The only thing he needs to do is to buy all that mining hardware.... Oh, and to produce some blocks... the cost of which is superlinear in the number of blocks... Mmmm....