Common law has the concept of "under duress". I'm sure other legal traditions have something similar. It is also common sense in the US culture in general that you can't be said to agree to having your legs broken in a situation like that.

While the mythical "homo econominus" may say that there's no difference between "give me $$$ or I'll inflict severe negative utility on you" and "give me $$$ or I'll reduce the positive utility you receive from selling goods by the same amount" by saying it's the same amount of utility in absolute terms in both branches, in practice nobody feels or operates that way, and that's with steelmanning this argument by declining to note all the obviously relevant ways in which this metaphor is a mismatch.