P2P technologies allow end users to provide bandwidth for file sharing instead of relying on large central servers that cost the content providers money. I frequently use Bit-Torrent to grab ISO images for Linux installs. Some people break the law using cars or guns, but we do not outlaw cars and guns - we just punish people who use them illegally. It should be the same way with P2P: if someone makes copyright movies available, that is wrong, and should be punished. Making the technology illegal is also wrong.
I think that one reason the big media companies lobby Congress to outlaw P2P technologies has nothing to do with current illegal use of these technologies. Instead, I think that they see a long term threat as entertainment markets are opened up to independent producers who find that their production costs are slashed using digital media and close to free distribution via P2P. A lot of people do not seem to mind commercials in network TV so why not fund Indy movies with a few embedded commercials? Same idea for musicians: produce low cost music videos and distribute them via Bit-Torrent (and if they get to be popular, add a few short targeted commercials).