There is another disturbing aspect to this:
If it is established that in order to avoid liability, providers must disconnect their customers after a certain number of allegations of infringement (because let's face it, it's rarely going to be practical to determine the factual or legal basis of these alleged infringements), then a new business model is opened up for copyright trolls. If they can obtain lists of email addresses of consumers, then they could send letters to those consumers directly, threatening to send a notice of infringement to their ISP unless a certain amount of money is paid. It would often be in consumers' interest to pay up, to avoid the hassle of disconnection from the internet.
Or they could send the letter to the ISP directly, and come up with some mechanism to pressure consumers into giving them money to avoid future notices or to somehow get the original notice rescinded. People won't know whether the activity really came from their IP address or not (e.g. their router might have been hacked), and it won't matter since it will hardly ever be worthwhile to bring it to court.
The threat of taking people to court isn't usually credible, but if a disconnection policy is in place, the threat of disconnection will be very credible. So the trolling business becomes much more lucrative due to higher rates of response. And what are the rules, if any, on sending multiple separate notices for infringements that occurred on the same date? Suppose someone's computer is hacked or they start using a file-sharing application, and they download multiple files on the same day. Could a legal firm send multiple separate notices to the same individual, triggering the disconnection policies of their ISP right away unless the individual were to pay up? It seems very possible.