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.