Someone may correct me if there's more to it, but I think it's just that some people are uncomfortable with Google having so much access to information about us. Any DNS server you access will have the potential to keep records of which IP addresses made which queries, which potentially gives Google even more tracking data. As far as I know, there's no real sign that they're using that data, but to some extent, they're a company that makes money from collecting data about their users, so...
I just happen to use and dare say trust Goggle, no matter what search engine you use with the exception of https://duckduckgo.com/ will track you. I do read the ToS's and privacy policies of any site I'm about to register on it's the data collected that your being informed of, I've refused to register on some sites over it or had second thoughts and bailed (Microsoft's Insiders program).
It's many features or abilities is why I use Goggle - and they give back to the community, the only company I know of that does it on their scale, Goggle Earth while very useful was first seen as incredible; it's now Goggle Earth Pro.
Above all you have to remember they make their living off of your data, Goggle Earth Pro was once sold (mostly to companies doing demographics), it will show you the tax assessment of every building I've check but one. I have an unlikely video hit on youtube.com the demographics given me are vast, and varied - while myself I'd never put an ad or overlay on any video; it's interesting the ages of people who are most likely to participate in a specific activity.
Bottom line, I trust Goggle to a point, as I won't use their DNS's, while tracking is ok within reason, I don't need to give it to them, and what's collected going through their DNS's? All ToS's and such claim unidentifiable information (but they've got your IP address) they don't need to know who you are, just your interest. There's a reason another Goggle sever center is being built, they need more space for what they do.