What is the flaw in this if any?
Rational self-interest. Study some game theory and try again.
You don't need to study game theory for this, simple common sense tells me that if it works I can make profit, suppose I have 10000 btc and I want to take sell them (say booking profit after a long run), but instead selling them all I will sell 9000, then use 1000 to bring the network to halt so that exchange rate crashes, and buy my 9000 back, so I have now lots of cash and almost same number of bitcoins and in medium to long term bitcoin price will come back after may be few fixes to protocol, as they always had