It can be, sure. But a two-way deal might also affect third parties.
Example: what if Adleman hires Rivest to put laxative in Shamir's soup? Two consenting parties have made a deal. Shamir freely chooses to eat his soup, despite knowing that he has only imperfect information.
So that scenario works out as desired.
But intrusive government regulation might come into play. Maybe the state prohibits poisoning soup. That harms the free market, and it's wrong. But, perversely, Shamir might benefit (at Adleman and Rivest's expense).