Sorry but no. Interpreting an IP address as identifying a user isn't a matter of interpreting the spirit of the law it's simply making a factual error. Should an IP address be sufficient to allow a search to be made? Certainly in a criminal case.
It is similar to the case of catching a speeding car but not being able to identify the driver (except speeding isn't a tort). You can't assume the owner is guilty unless the law is drafted to make it so that a car owner is responsible for all authorised use of their vehicle.
Talking about the spirit of the law is considering the law makers intentions and how they would have drafted the details in the current technological background.
Even if you narrow down the guilty party to one of a small group you can't convict the whole group or even a random member of the group on that strength alone. That's not how European or USA law works (though there may be other crime, withholding evidence, harbouring a criminal and such that members of the party would be guilty of).
I wasn't arguing the letter versus spirit in terms of the IP address. I was more arguing about piercing the corporate veil. By the letter of the law, the infringement may have been made by the company, but, by the spirit of the law, it's clearly made by the person.
However, I want to take your speeding car analogy a step further. The police have video of my car parked outside a murder scene during a murder. The murder was performed with my handgun. On the 911 tapes, the victim is shouting that he's being attacked by someone with my name (John Smith). The victim is someone I've previously stated that I intend to kill. The argument that none of those identify me aren't going to form a reasonable doubt unless I can also provide an alibi or implicate a different John Smith.
In the same way, the original poster has publicly stated their intention to start an open network for the specific intent of hiding their downloads. The MPAA has an IP address that shows that a download was made from the account that was purchased by a person intending to hide downloads. If they have server logs showing that other people use that network on a regular basis, they have a decent chance. As it stands, however, it's pushing the bounds of reasonable doubt, not to mention preponderance of the evidence, as needed for a civil case.
It is similar to the case of catching a speeding car but not being able to identify the driver (except speeding isn't a tort). You can't assume the owner is guilty unless the law is drafted to make it so that a car owner is responsible for all authorised use of their vehicle.
Talking about the spirit of the law is considering the law makers intentions and how they would have drafted the details in the current technological background.
Even if you narrow down the guilty party to one of a small group you can't convict the whole group or even a random member of the group on that strength alone. That's not how European or USA law works (though there may be other crime, withholding evidence, harbouring a criminal and such that members of the party would be guilty of).