Charging by the GB is one of the fairest schemes because if it was about usage (i.e. the non-stop-Youtube-watching-bogeyman), then charging by the GB would let them get a fair share.
That net neutrality means that you can't use the network even though it would be available bothers me from a hacker perspective. In that sense it seem much better if there were no "speeds" or "GB" at all and you or the services pay for priority. (which probably isn't how it would play out)
In such a scenario, I would prefer to be billed by the GB, which in my mind is a honest and transparent mechanism for usage. Loss of net neutrality, in addition to all of the other evils that have been mentioned elsewhere in this growing thread, puts yet another power lever in the hands of the duopoly and away from the consumer hands. Why do I think this is bad? Because I have no confidence that once the ISP duopoly has control of traffic prioritization, they have any incentive to dangle it in front of the consumers when it is likely more lucrative to cut a deal with a content provider to force feed the consumer ad-based content vs. paid ad-free content.
Since you can't favor certain services that mean you can't favor them even if it's warranted. Say you are charged per GB and one video startup only have servers in another country, while the other is using a caching service at a local data center. It would 'cost' a lot more for the Internet in terms of infrastructure to get that data from the other country. But your ISP still have to charge you the same in GB for each service.
Since you can't favor certain service you also can't faster connection for only some data. Say you are paying for a 10 Mbit connection and buy a game for download. Even though you only need a fast connection for a certain amount of time/data and you've already paid something, there's no way to for the provider to buy high speed data to you. Instead you permanently have to get a faster connection just to have a good experience with service you are already paying for.
Not differentiating different traffic and/or paying per GB enforces this old notion of having your own connection to the Internet. Today there's Internet everywhere, there's few reasons why you should be able to access your services or ISP from other connections. If an ISP can't discount, or even bill, some traffic it's harder to share the connection that already exists with other parties.
As long as there's a monopoly/duopoly they will always charge you, but instead of charging you directly for Netflix traffic they charge you for a faster connection or data overages.
The ISP can't choose for you which services/end-points get favored.
You could get a 10 Mbit/s flat and 100 Mbit/s volume with some User interface to choose "Everything to the flat, [super awesome online shop for games] to the volume"