No, it isn't. You're making the huge assumption that both parties are equal in the exchange and one party isn't using force on the other. Again, typical libertarian fantasy assumes everyone is nice, wake up, they aren't.
It doesn't require anything you name here except the absence of force. No libertarian thinks or assumes everyone must be nice and no libertarian thinker has ever predicated his argument on such.
You know, there actually have been some highly intelligent and thoughtful libertarian thinkers, far from whatever fantasy you may have.
