I understand that. The sentence is still not true. For example in world economy if you buy oil from ISIS for half the price they believe they have gained, you b

I understand that. The sentence is still not true. For example in world economy if you buy oil from ISIS for half the price they believe they have gained, you believe you have gained and people they are going to kill with newly acquired weapons believe they have lost. There is overall loss from this transaction even measured by what people believe they have. That's why it's valid to consider questions as if should drug trade be allowed and to what extent as ethical questions even if you believe that you shouldn't force any value system on parties making those transactions.