Enforcement isn't actually impossible, though. You certainly can't kill piracy entirely, but you can make it difficult and dangerous enough that most people won't bother, in the same way that China makes avoiding censorship difficult and dangerous enough that most people don't bother.
I am not remotely convinced that would actually help the entertainment industry (although it probably would help the really big companies a bit, especially the ones that are feeding off past success rather than producing things that are actually good), but I think that it is possible to make piracy on a large scale not be worth the risk.