There's a fundamental difference between physical property and intellectual "property": an owner of the former can conceivably hire guards to protect or restrict access to that property, since physical objects are generally localized phenomena.

But there is no conceivable way to enforce things like copyright or patents without something at least as powerful as a government, since they are supposed to be binding on every single person, everywhere, all the time.

IMO the concept of "intellectual property" is at best orthogonal to that of a "free market".