It seems like they always want to go after the ISP. What about the phone company that provides the wire? What about the power company that provides the electricity? Or any other of a number of utilities and companies that provides services to this person?
If I were making illegal widgets, would the company being infringed upon go to the local store where I bought my parts? Again, what of the other number of utilities that provide service to my residence or place of business.
Why should any one of these be held liable just because someone comes to them and says I think someone is doing something illegal and I can sort of prove that is was them or at least someone that lives in the house or possibly neighborhood?
ISPs are no more authorized, nor should they be, to act as law enforcement than any of these other companies. If it is a legal matter, than the police/local authorities should handle it.