You state yourself that the ISP also has the service address, and it's also clear that everybody in the house is using the internet connection, not just the person who is paying the bill.

So identifying the customer provides the ISP with neither the identity of the person using the internet connection, nor any more information (than the service address) about how to locate the person using the internet connection.

So, even if you believe it is right and proper that ISPs are deputised to track down internet users on behalf of the government: why is it advantageous that they identify their customers?

Um, if someone drops a bunch of child pornography from your Comcast account, very upset people in suits are going to talk to (and very likely arrest) the accountholder, which is you, first. An accountholder is responsible for what takes place using the service, just as if you were to hand your phone to someone and they call in a bomb threat, or you lend your friend your car and they go rob a bank with it. They're going to talk to you first, and your house doesn't matter. That's not "deputization." That's accountability for actions utilizing a service that is able to touch other people. That identity is not revealed until an alleged crime meets the minimum bar to subpoena the provider. Nobody is asking Comcast to go looking for you.

I'm not sure what logical point you're trying to make. They've identified the user of the Internet connection; the user is the accountholder. The strong identification of that accountholder follows them if they disappear, which is useful for both receivables and security/LEO. That's the advantage.

> just as if you were to hand your phone to someone and they call in a bomb threat

Nope. In that case you are entirely clear unless you knew their plan in advance and still let them do it.

> Or you lend your friend your car and they go rob a bank with it

Same as above

See the Ryan Joseph Holle case from 2004

I said they are going to talk to you first. I didn’t say they are going to convict you.