Is it that obvious?
Would you accept your car to collect anonymous driving data without your prior consent? Would you accept your OS to collect anonymous usage data without your explicit consent?
Why should we accept our online behavior being analyzed anonymously without actively giving our consent?
This is not a question about the current state of the law; it is not about its past and future evolutions. It's even less about legitimate interests. It is about individuals, at first, and their absolute right to privacy.
Shouldn't the consent be central, mandatory, and inalienable?
To me this means data like number of page views over time, etc. It's information that you get in the course of operating your service and that does not involve any personal data.
At the most basic your car does collect "anonymous driving data": It collects the distance travelled at the very least and most modern cars also work out an average MPG based on that.
"Privacy" needs to be defined here. In general the term relates to personal data. I have a right to be anonymous and left alone when I walk in the street, for instance, but others are still free to e.g. count me if they want to make statistics on how busy a street is.
The issue is with enforcement. Lots of today's data collection, sale and use is illegal (often patently so).
Isn't that exactly what Windows 10 is doing?
What stops an individual from having a scrapbook of observations they made of people?
What stops a corporation or intelligence agency from doing the same so long as they don't advertise they are doing it?
Is there any right to transfer huge sums of money internationally anonymously when that is a channel for kleptocrats to steal?