The phrase "if buying isn't owning then piracy isn't stealing" is fundamentally true but it doesn't go far enough (partly because piracy was never stealing to begin with but that's another topic). I'd say if buying isn't owning, then piracy is a means of defending your property rights. Just like nobody has the right to reach into your pocket and steal physical property from you, companies have no right to do the same with a digital good that you purchased from them. Piracy is an anti-theft measure.