The decision to blackmail is made in the hope to gain something by you responding. If the blackmailer knows that you won’t respond, their expected gain is drastically lowered, and they will probably decide to do something else instead (“something that takes less effort”). I suggest that maybe this is what we could call the “default”. So if your expected utility is lower in the “default” case it’s bargaining, otherwise, blackmail.
However this definition would call an offer “bargaining” if the “default” was to do something else (more) harmful to you, which I’m unsure is correct. But it does make “don’t respond to blackmail” rather tautologically true.
The decision to blackmail is made in the hope to gain something by you responding. If the blackmailer knows that you won’t respond, their expected gain is drastically lowered, and they will probably decide to do something else instead (“something that takes less effort”). I suggest that maybe this is what we could call the “default”. So if your expected utility is lower in the “default” case it’s bargaining, otherwise, blackmail.
However this definition would call an offer “bargaining” if the “default” was to do something else (more) harmful to you, which I’m unsure is correct. But it does make “don’t respond to blackmail” rather tautologically true.