Indeed someone rights are being infringed
and those are the rights of the copyright holder not to have their work blatantly copied around the internet with no consideration of their wishes.
However I do agree that cutting off a shared service means that someone other than the perpetrator will suffer. Just as others, I have my concerns, people should not be cut off simply because the copyright holder believes their rights are being infringed. If they have some evidence that a specific IP address is hosting their material then hand that information over and then let the police follow the matter up.
I'd be all for the idea of a warning, the commonly mentioned three strikes (which must be punctuated by warning letters). It would then be up to the householder to restrict access to the internet for the perpetrator. If they cannot do this, or are unwilling to then yes the entire household will suffer.
But I hear the cries now "The Police should be out catching real criminals". This was the old war cry of the drunk driver and those that liked to drive recklessly.
Let me put it another way. Suppose your household has a shared car. The 18 year old takes the car out, parks illegally and gets clamped. You are all going to suffer then too.