Well, if we make your example into something more sensible:
Say you walk into stores and threaten to sue them for $8000 if they don't pay you the $3000...
Then there's nothing really wrong with that. You're not really exerting any undue influence or behaving unconscionably - just exercising your right to file suit. If you genuinely believe that the suit has merit (as the RIAA does), then them signing the contract as a genuine compromise is legal and really quite commonplace.
I don't really see the problem with this.