To counter azxcvbnm321's argument, let's look at Metallica's attack on Napster as an example.
In a world without pirating, only Metallica fans and heavy metal fans would buy a Metallica album. Perhaps through constant support from mainstream radio stations, they may be able to lure in a few listeners from other genres to buy they albums. But realistically, only those people into Metallica in the first place would be listening to their music.
Enter the real world where pirating does exist. Now, a non-Metallica listener can download a song or five, or an entire album and listen to it without having to pay for it. What does that mean?
Metallica fans will still buy their albums. Heavy metal fans will still buy their albums, so their sales aren't affected by that. But those people, such as 13 year old girls who would never dream about buying a Metallica album, may suddenly be sporting Metallica songs on their playlists. Since these people wouldn't have bought a Metallica album in the first place, this has no bearing on sales. But it does garner Metallica new fans from demographics they may never have dreamed about. And perhaps, these same people may end up buying future Metallica albums.
Instead, all Metallica did was shut these people out from listening and getting into their music. Again, these people never would have bought a Metallica album in the first place, and now, they most likely never will.
There's no stealing involved. There's no resource being consumed. These people are not taking money out of these musicians' or developers' pockets. We're talking about money that never would have been spent on these albums or games. If they were given an opportunity to get into that music or game, without risk or limits, perhaps those musicians and developers might garner more fans and more profits in the future.
Of course, if you were going to buy a game or album, but instead just downloaded it without paying, then you are denying the developers and musicians or a sale, and thus that would be taking money out of their pockets, and that's wrong. But if you were never going to buy it in the first place, I don't see what's wrong with that.