Protecting intellectual property rights?

Well, shoplifting I think is a crime because you are stilling something from the store, not for the IP rights on it.

Downloading something available for free could be arguable. If it's available for free, obtaining that piece of information alone may not be criminal in every case; whereas sharing something illegally without copyright certainly is a criminal act without doubt.

Also dealing with what's been downloaded could bring other legal complications. E.g., recently Comcast tried to detect torrent users who used torrent to download contents that may or may not be illegal, but was sued for privacy instead.

Many music distributors tried to control online music distributions by limiting MP3 copy cycles and etc, but they also gave up controlling that since piracy technology was way ahead. It will also be very tough to monitor all the piracy download websites since there are so many of them in servers all over the world where there is not enough digital legal presence.

I personally think the distribution channels and revenue generation would change rather than waiting for the audience to change. For example, I expect singers to rely on concerts and performances more and more to generate their income than album/music sales. In return, concert ticket prices might go up. For music distributors, they might be offering CD/MP3 files at a very low cost (I think it's already low though) and would ask for a share of concert income instead.