It's proof time! A professor at the Hong Kong University of Science and Technology has written a paper on how DRM makes buying music less attractive.

We look at the firm's optimal choice of Digital Rights Management (DRM) protection, and find that revenue decreases with increased protection, and so it is optimal for the firm not to employ any DRM, in the absence of network effects. Listening to music or watching video protected by DRM is cumbersome to users. They have to download license files, there are restrictions on the number of times the file can be copied, and restrictions on the type of devices that can play the file. As a result there is a disutility to the legal consumer, because of which the firm charges lower prices. Loss in revenue due to decreased prices cannot be compensated by the increase in demand, and hence revenue decreases with higher protection.

Thanks to Earnest for the tip.