Doom 3 being available on P2P is really fine if you ask me. It is NOT piracy. Is it right? Maybe not, but the word piracy is way too much of an extreme word to use regarding something like copyright infringement. Piracy was the act of violent robery on the high sea which involved murders and other nasty violent things!!! SO there is NO way in HELL you can refer to something non-violent and non-physical as piracy!!!!! It is nether theft nor stealing. It isn't right, but the appropriate terms must be used to define how wrong something is. Stealing is when you take something from someone else so that no longer have it in their possession.
Well, anyway, it is good to buy games to support the developers of them so they can continue to produce new games and to reward them for their hard work. And even though people will be able to obtain free copies without having to support the makers of the game, it really isn't going to hurt them at all anyway because you really have no choice but to buy the game if you want to play online as all games these days require a unique CD key that is authenticated with their server to play online and you have to be online connected to their servers, and there is really no way around it. So you are SOL if you want to play online, and didn't purchase a licensed copy of the game and will be restricted to LAN games only.