Lets get this straight. Piracy is not theft and theft is not piracy.
Sure enough the two are related concepts but it's wholly inaccurate to classify one as the other. While in the eyes of the law they are both crimes, piracy is one that average people are more ready to commit. Why is that? Namely it's because they don't see the harm in it. If you steal an old ladies purse then that old lady no longer has her purse. Where is she going to put her knitting now? Reasonable people feel guilt over performing such actions and often go crazy from the clickaty-clack of the knitting needles echoing throughout their conscience.
However, if you were to take an exact copy of her purse then she still has somewhere to put her knitting and you'd have half a scarf. Everybody wins. Except of course now you'll never buy her scarves at the weekly jumble sale and she won't be able to afford that trip to Florida any more. Of course most people don't think that far ahead so they'll live quite happily with their ill-gotten gains free from guilt and those pesky haunting knitting needles.
Theft basically boils down to the removal of value. You take something valuable and someone else no longer has that value. It has been irrecoverably (unless they arrest your thieving ass) removed from the system. With piracy though the original value is never removed. What changes is the potential levels of value. And unlike theft piracy can actually result in a gain of value for the victim of the piracy. This I believe is the biggest factor that differentiates piracy from theft, it can actually have a positive effect on value.
Lets revisit our old friend the old knitting lady for some scarf themed examples of the three potential effects of piracy:
1. Negative potential value
This sadly is likely the most common form of piracy and is generally why it's considered theft as well as an all round bad thing. Take Mr Bastard now. Mr Bastard would normally purchase a scarf from the dear old lady but upon finding out he can receive a magical scarf duplicate ends up not doing so. In this case a potential sale existed but then was lost due to piracy. The old lady has lost potential value. And she is sad.
2. Neutral potential value
Probably the second most common form. Take Mr Apathetic. Mr Apathetic would never consider purchasing a scarf from the dear old lady. However he will take a copied one for free. If he couldn't get it for free though he wouldn't purchase one. Here no potential sale existed in the first place so there is nothing lost, nothing gained. It's still not morally correct but the victim has technically lost nothing. The old lady has lost nothing, gained nothing. She is knitting.
3. Positive potential value
What's this? Positive piracy? Surely not! Piracy is a bad dirty crime for thieving bastards I hear you cry. But consider the case of Mr Unconvinced. Like Mr Apathetic he never considered a scarf purchase. However upon trying a free copy of it he comes to the realisation that he really likes it and pays the old lady her due. Here this is a sale that previously didn't exist in potentia but was created through piracy. The old lady has actually gained value from this. She is off to Florida.
This isn't an endorsement of piracy nor is it showing that it's morally acceptable. It's merely an illustration that it's more complicated than simple theft and how the two actions should be considered independently of each other. It's not such a black and white concept.
Unlike this Jolly Roger I'm knitting.