Chumbawamba have posted a great editorial on their site about why their CDs don't have DRM on them:
Well, I'm not one to believe statistics and the like, but most recent independent research clearly shows that these same people who illegally download music on P2P networks also spend more money on legal downloads (from sites like Napster, iTunes store etc..) and buying CD's than those people who don't venture into this shady world.
History has a habit of repeating itself – consider some earlier examples of the Music Business getting hot under the collar:
Early US records (eg Brunswick Records, who released, among others, Robert Johnson) had "Not for play on Radio" stamped on them, for fear that radio play might harm Sheet Music sales.
Later, in the 1970's, the Record Business claimed "Home taping is killing music". Don't make me laugh – home taping was a fantastic, free way of promoting records, just as Radio play (and P2P file-sharing) is.