I would counter that it isn't necessarily always morally wrong to steal. Suppose I need some medicine to survive and I have neither the money for it nor the ability to get the money legally. I would argue that since I will die if I don't get the medicine, it's then morally acceptable to either steal the money necessary to purchase it or to outright steal the medicine itself, provided doing so doesn't have the foreseeable consequence of putting the victim of my theft into a similar life-or-death situation.
Would you agree that in this one situation, theft can be morally justified? If not, then say there were 10, 100, or 1000 people in need of the medicine; is it OK to steal to get it then? If not, is there a particular N such that it's OK to steal to save N people? It's just not that simple, and saying "stealing is immoral" doesn't cut it (IMO) as an argument against piracy, even if you buy the argument that piracy == stealing.