"If it's only encumbered by the copyright and patents of the user (which is the case much of the time, because all rights are often waived), then it's free."

You can't guarantee that in the us. We're not even legally allowed to show someone a work with a copyright claim. We can't even reproduce a patented thing whether we knew it existed or not. Copyright and patent trolls increasingly sue businesses to the tune of billions of dollars. The risk is there so long as the system works the way it does.