Sure. But if you have an argument that some guy who shows me apparent magical powers has the power to torture 3^^^3 people with probability substantially over 1/3^^^3, then I bet I can turn it into an argument that anyone, with or without a demonstration of magical powers, with or without any sort of claim that they have such powers, has the power to torture 3^^^3 people with probability nearly as substantially over 1/3^^^3.

Correct. That still doesn't solve the decision theory problem, it makes it worse. Since you have to take into account the possibility that anyone you meet might have the power to torture (or reward with utopia) 3^^^3 people.