Well... I said "some ISPs" sell your data, not "every ISP", but I wouldn't put it past any of them. Personally, I don't trust cloudflare, I don't like efforts to kill ad-blocking, and I don't like further consolidating people's DNS traffic into the hands of a smaller and smaller number of providers. I've got the feature disabled for now. I wish someone like EFF would set up a DNS server supporting DoT. I'd pay for the service!

ISPs don't have the best profit margins, especially ones in competitive markets..

If the big players are selling DNS data, I guarantee you there are companies out there approaching every other smaller ISP with a turnkey solution that makes it as easy as possible to do the same thing with some kind of revenue share model.

Not a lot of businesses would turn down extra money like that, when they know their big competitors are doing the same thing.

Unlike most ISPs, privacy and security are a core part of Cloudflare's brand and business model - at least at the moment - so it's in their own interest to actually not do this stuff.

Only time will tell whether or not they pull a "don't don't be evil" on us, but that's a different conversation. :-)

Cloudbleed and particularly Cloudflare's response to it (the way they publicly blamed Google) tells you everything you need to know about how trustworthy Cloudflare is. I personally use Google via DNS over TLS, not that it is a good option but I personally prefer that to the alternatives available near me. CenturyLink was intercepting DNS last I checked a few years ago.

Cloudflare promises that they don't in a legally binding document. Does your ISP do the same?

It is much easier to replace Cloudflare if they violate your privacy than to replace your ISP if they violate it. That helps to keep Cloudflare honest.