I always find that kind of comment quite amusing indeed. Recording and distributing copyrighted live material is illegal anyway. Back in the day you sometimes had a copyright note on bootleg CDs.
Now I really can't see how you can stop anybody from sharing something you shouldn't have in the first place.
BTW, I do know it's a moral issue rather than a law issue.
To the best of my knowledge, if you tape live material, this isn't copyrighted, as copyright exists in recordings. If you were right, recording a show you've been to and listening to it at home would be illegal. You're not allowed to sell it, though. Also, I see a point in not spreading lossy versions, since these will inevitable deteriorate each time they're transcoded. Keep the trades lossless, and then you can do what you like with them yourself.
Niemand hat die Absicht, eine Mauer zu errichten.