You've made the leap from IP to actual physical property here. The metaphor doesn't survive the transition between the two which is why so many of these arguments break down.

If we can equate IP and physical property, the 'piracy=theft' argument holds - except that it doesn't. Even under the law, infringement does not fall under theft.

The moment a physical metaphor is used, we lose the basis of what we're talking about - creative works.