Assume that Draco and Harry both value victory at $1000. Now if you demand $800 from the winner, the loser “would have” gained only $200 in the counterfactual case, so he will pay you $200 at most. So you could have just demanded $1000 minus epsilon from the winner. We could probably prove a theorem that says counterfactual mugging can’t help you extract more of the surplus economic value that you create.
Excellent point! This is what I get for posting in haste.
ETA: However you can extract more than $1000 if you assume that at least one of Harry and Draco would rather the other of them win than Hermione. No counterfactuals needed.
Assume that Draco and Harry both value victory at $1000. Now if you demand $800 from the winner, the loser “would have” gained only $200 in the counterfactual case, so he will pay you $200 at most. So you could have just demanded $1000 minus epsilon from the winner. We could probably prove a theorem that says counterfactual mugging can’t help you extract more of the surplus economic value that you create.
Excellent point! This is what I get for posting in haste.
ETA: However you can extract more than $1000 if you assume that at least one of Harry and Draco would rather the other of them win than Hermione. No counterfactuals needed.