>the logical implication is that mutual agreements are equitable

But nobody uses 'equitable' in this sense, as people have a variety of reasons to engage in a mutual agreement, where upon asked one or even both parties would agree that the agreement isn't 'equitable' or fair. To say that mutual agreements are equitable is only because of the assumption that the agreement wouldn't have occured or been accepted if the agreement isn't equitable - which is obviously false, given that people agree to heavily unfair (though not unconscionable) contracts all the time.