Okay, I just typed out a motherfucker of a long post and deleted it. I don't want to get into a huge ongoing argument about this or anything, so I'll just keep it short.
Metallica cracked the shits with the downloading of their music, as did a fair share of other groups when the whole Napster shit-storm started. Other bands who actually put some real thought into the situation took a more mature and pro-active approach tried to work with what was happening by talking up the promotional value that mp3s can have and offering their own for download. Metallica, however, got very vocal about how awful it all was and how it had to be stopped etc. etc. If memory serves me correctly they tried to (did?) file law cases against people who had downloaded their music and sue them.
At the time (because I don't know if this is still the case), Metallica were recieving $4 or so per CD sale... a figure that was/is practically unheard of for most musical groups. I'm pretty sure that they were getting roughly 3x more than most 'big' bands per disc, and possibly the most money of any popular artists at the time.
They can't stand to lose some cash to MP3s, but they're perfectly happy to spend a bunch on trying to fuck over a handful of people (their own fans no less), many of which probably wouldn't be able to afford the legal fees and such if they had to.