Who cares?
Markets present opportunities for this. If someone wants to risk their assets and try to send signals about demand/supply to drive others behavior, so what? All parties involved are freely choosing to take the actions they take, and all parties know the risks.
Attempts to regulate this kind of stuff only puts a corrupt, inefficient structure in place of what might emerge as self-regulating adjustments by all parties.
RE: Mysterious Trader With "Nearly Unlimited Bankroll" Said To Manipulate, Dominate Price Of Bitcoin