I'm going to have to respectfully disagree with you there. If you're having to research the history of the phrase, you're overthinking it. It means exactly what it states, no tricks. "Free speech" is a well known phrase that means the unencumbered ability to say what you like. "Free beer" means something that everyone (ostensibly) likes being handed out without the need for payment. I'm not sure how one could more simply explain the "free" dichotomy. If you've got a suggestion, I'm open to hearing it.