When you create a Google account, you're asked to provide your name, your gender, your date of birth, your location and your mobile phone number. Some of your most personal and private details, all of which will now be tied to your online behaviour.
That ceaseless data capture starts right from school, where millions of students use a cloud-based OS called ChromeOS that records everything they do. It's quite horrible that this is happening - the kids don't even get a say, it's the adults who've decided this.
It doesn't matter if that information is only collated in aggregated form and detached from user accounts, we don't know how that information could be mined or analysed either now or in the future. (In fact, I suspect that even Google hasn't figure all the possible uses of the ginormous quantity of user behaviour it has captured and continues to capture).
And we've seen from Spotify and Netflix how even aggregated data can reveal very private and personal user behaviour.
Google and many of it's supporters conflate security with privacy. Just because Google hasn't ever suffered a breach of user data, people say that Google can be trusted. You can't have privacy without security, but security by itself does not equal privacy. You're still being tracked relentlessly by Google no matter how securely it's storing your online behaviour.