So is robbery blackmail? "The status quo is not to harm or steal. Give me your money, or I will hurt you and take your money." Wouldn't most crimes fall under the same definition?
In fact, isn't the social threat of negative publicity just blackmail against would-be public adulterers? "-affair for A, +prudish satisfaction for Bs" or "-status for A, whatever Bs get out of shaming A". And justice is probably just blackmailing people into being nice against the status quo of natural selection to avoid punishment...
The robbery case is certainly blackmail according to my definition. I agree it sounds strange to call it that way, but I am quite happy to call it "extortion". And I think the distinction between blackmail and extortion in ordinary language (is it that in blackmail the threat must be to reveal information? I'm not sure, not being a native speaker) is slippery and of little theoretical significance.
The other two are not blackmail because the status quo I am talking about is an actual state, vague to define but roughly composed of the reasonable ex...
For a more parable-ic version of this, see here.
Suppose I make a precommitment P to take action X unless you take action Y. Action X is not in my interest: I wouldn't do it if I knew you'd never take action Y. You would want me to not precommit to P.
Is this blackmail? Suppose we've been having a steamy affair together, and I have the letters to prove it. It would be bad for both of these if they were published. Then X={Publish the letters} and Y={You pay me money} is textbook blackmail.
But suppose I own a MacGuffin that you want (I value it at £9). If X={Reject any offer} and Y={You offer more than £10}, is this still blackmail? Formally, it looks the same.
What about if I bought the MacGuffin for £500 and you value it at £1000? This makes no difference to the formal structure of the scenario. Then my behaviour feels utterly reasonable, rather than vicious and blackmail-ly.
What is the meaningful difference between the two scenarios? I can't really formalise it.