While I somewhat agree about the tracking (if every device gets a /64, then, while the device can chose the host part, the network part is fixed, so site owners would just track the network part to uniquely identify a device or subscriber), I don't see the argument about illegal contents.

To track a downloader of illegal content, you'd still have to go through the users provider and the provider can easily determine who actually downloaded that content at a time.

So as long as providers cooperate, it's not easier or harder to track down a pirate with IPv6 than it was with IPv4