And what if XYZ does violate the contract? How harsh would the penalties be in absence of a government-sponsored MPAA racket? Yeah, you could draft a contract that said "if you leak the film you owe me $100 million compensation", but good luck finding a theatre chain who would be prepared to take that kind of risk. On the other hand, if the mutually agreed penalty was more market-realistic, say $1 million, that would no longer serve as deterrent onerous enough to prevent a leak. All it takes is 1 out of 10,000 employees being careless, or dishonest, and the damage is irreversible. XYZ would not bother investing millions in airport-style security scans for every cleaning lady that enters the cinema building. It would simply accept the risk of paying the penalty.
Right, so there is a point in your example somewhere between $1 million and $100 million where the theatre owner and the film producer can come to agreement. Some point where it is feasible to take the movie and risk it getting out in the world and duplicated for free, and some point where the theatre operator can make money showing the movie even if he has to pay the fine.
The point is, somewhere along the line somebody is going to have to violate a contract in order to have the movie available for 'free'. Either the theatre owner is going to start making copies, or a person who viewed the film, or an employee of the theater. In a society of all libertarians, someone is going to have to violate libertarian principles in order to supply a free movie.
Therefore it does not make sense for present-day libertarians to advocate piracy, or using bitcoins to facilitate piracy, in the pursuit of libertarian goals. At least not in the context of the present discussion around movies. Maybe things are different regarding software, drug patents etc.
At no point am I saying that if A and B create a contract, C is somehow obligated to follow the contract. I am just saying that for a large number of scenarios A and B can create a contract in such a way that the likelihood of C "somehow" acquiring the IP for free is very low. Or at least B will have to compensate A in such a way that even if C gains access, A won't care.