I produce electricity, which is immaterial, at the cost of my resources. Are you legitimate to plug your stuff on my power cable without my consent? According, to the "Libertarian" ideal, you wouldn't be stealing my power cable, only the energy it conducts. We can all see this is going to end bad.
This isn't a valid point. You can't bring is a purely pragmatic point into a fundamental discussion. The point isn't who is harmed the most, the point is "Is the product of my mind my property".