Exactly. It's double dipping to charge for the rate of flow and the amount. We don't do that for water.

The only reason the major ISPs want this is because the old content providers are desperate to maintain their positions in the market. They think they can squeeze out competitors by joining forces with the biggest ISPs [1] and implementing zero rating and data caps. That way no one will be able to compete with them. You won't want to pay for your overages on the next Netflix when the current one has a free-pass arrangement with your regional-monopoly broadband ISP.

[1] https://en.wikipedia.org/wiki/Acquisition_of_NBC_Universal_b...