[kmeisthax]

I can see why entirely unrelated ads could be seen as a bad thing... but the problem with FLoC - or really any ads personalization - is that it's fundamentally based upon a privacy violation. Ergo, even if the data is only being used to serve more relevant advertising, you're still trusting some process or third-party not to use your data for more nefarious purposes.

FLoC is not immune to this: it relies on the device being able to track users and then provide advertisers "blurry" access to that tracked data. The problem is that we already have plenty of other tracking mechanisms that we can't reasonably restrict and that will interfere with the privacy protections built into FLoC. You will always be able to fingerprint and FLoC will always provide some fingerprintable entropy.

Even if FLoC was trustworthy enough to do what it claims, your interest cohorts alone can reveal your secrets. There's the classic example of Target knowing a woman was pregnant before her father was, for example. Yes, Google is going to try and filter out sensitive interests in cohorts, but that's an additional layer of trust you can't control. What if Google's definition of sensitive interest differs from yours?

[visarga]

They give you cohort ID 0 branding you as someone with sensitive issues. That's just another way of disclosing information about us.