There's a very simple explanation: Rules are created to optimize outcomes, not to be logically consistent. That's it. People who think everything flows from a

There's a very simple explanation: Rules are created to optimize outcomes, not to be logically consistent. That's it. People who think everything flows from a small set of elegant axioms are wrong. Such systems never survive contact with reality, because reality is messy and not mathematically elegant. Rules are also created by multiple parties, in multiple circumstances, and with various compromises, tradeoffs, subjectivity and intentional and accidental omissions built in, which require later inelegant patches. The reason why blackmail is illegal though the components of it are fine is because we've seen that it leads to very suboptimal outcomes. It allows one to wield far more power than one would legitimately wield. If you reveal something embarrassing or illegal about your boss, your boss may be replaced with someone else. If you try to make an agreement with your boss without blackmail material you usually get a "fair" negotiation and outcome. The combination of both allows you to wield power you never could otherwise. And in general a situation where people who do stuff like installing spyware or digging through somebody else's garbage manage to usurp authority isn't a good one.