Imagine if I want to use photoshop. I consider it a piece of shit, I am not going to buy it (or rather I do not consider it worth my money). If I cannot pirate it, I will not buy it.
This results in $0 (zero) lost revenue from Adobe.
This is just an example, I do not use photoshop.
You will also get nowhere calling people thieves either. The image explains it simply. Piracy is not theft. It's Piracy. It's in many cases, copyright infringement. If I steal (actually steal here, not your definition) a loaf of bread from Walmart, I have removed it from their possession. They can no longer sell it.
If I make a copy of a file you have, it does not change your ownership of the file in any way whatsoever. Unless I told you I had done it, you might not even know. One does not simply copy a loaf of bread.
There's also the issue of DRM and draconian copy protection in software and games. They make it incredibly easy for the pirates to offer a superior, less restricted product.
If I cared about Assassin's Creed 2, I would pirate it and thus not be forced to needlessly ensure my internet connection remains stable throughout my (single player) play time.