We should stop arguing that AT&T should be legally barred from doing something with the data it has access to, and start making it so that AT&T doesn't have access to that data.
Why should we stop arguing that? The postal service operates under the same constraints.
The USPS analogy is a bit apples to oranges; the USPS is a government organization and AT&T is one of many private for-profit entities that carry our digital communication. Furthermore, AT&T already was legally barred from listening to conversations going through their network and they did it anyway. I don't exactly trust them, even if there are laws.
I don't think we should expect companies to not try to make money. Their function is to try to make money. If they see ways to try to make money, by asking consumers to pay extra for faster connections to Netflix, they should be allowed to offer premium services.
A big problem with the question of net neutrality is that it's subjective. It's fair to say they're slowing people down if they don't pay more. It's also fair to say they're just offering premium service for a premium fee. These is no winning this argument, both sides have valid arguments. Focusing on privacy instead will answer a question that has a clearer "right" answer, and it will automatically yield a network that has net neutrality built in.