This isn't some moral position, it's an economic one.
ISP's make money with the data they gather. Once you remove that as a revenue stream, it'll naturally increase the prices those companies are willing to charge.
They make more than enough money by providing the Internet service. They should have nothing to do with your data. Especially considering, how easily they can spy on you. It's like your post office delivery would charge you more, if they'll not sniff through your mail. This thing shouldn't even come up as a "feature", it should be the always enabled default.
The USPS likely would charge you more, if they weren't already in the business of selling both address lists and access (carrier route deliveries of bulk mail). So they might not be sniffing your mail, but from what it seems the postal service needs your data to survive.
That's why it should be a government service. No more tracking by private companies reselling your data to everyone and their dog. No more foreign governments selling you crazy ads.
It's obvious greed. There is no need to violate people's privacy for the ISP. Which you yourself point out. They don't do it out of need, but because they can.
ISP's make money with the data they gather. Once you remove that as a revenue stream, it'll naturally increase the prices those companies are willing to charge.