In my opinion, the difference with Google is that Google is actively using your data and you're giving them a lot of it. For Cloudflare, what do they have exactly? Depends on what services you use, but really all they get from me is the list of servers that connect to my domains. Google does that too if you use 8.8.8.8, or if you have any of their hardware that overrides router DNS settings like Chromecast and Google TV.