But Bitcoin is not a stock nor a commodity. It may be illegal at regular exchanges like CBOE or Nasdaq, but how is that illegal at Bitcoin ones? We don't even know what these exchanges are doing themselves, and whether they are not doing things like front-running the orders of their clients or similar stuff. Bitfinex is rumored to be printing virtual dollars out of thin air just like that. I don't know how legal that could possibly be. Though I agree that P&D groups are mostly scams, but I still don't get what's wrong with a tightly-knit group of people to exert influence on prices by massive buys or sells.
I'm sorry if I misinterpreted your statement. I agree that P&D in this case is not necessarily illegal because cryptocurrencies are not regulated securities (at least in the U.S.).
However, I am not talking about a tightly-knit group of people. The intended victims of a P&D group are the members themselves.