Why GA Consent Mode falls into a legal grey area?
Consent Mode is Google’s way of letting GA4 keep working when people reject tracking. Instead of stopping completely, GA4 sends small, cookieless pings and uses the behaviour of consenting users to predict what the others probably did (in Advanced mode).
Legal experts highlight that predicting behaviour after a user rejects tracking can be problematic. It does not go with the spirit of privacy-friendliness. This is why Consent Mode is seen as..
a grey area instead of a clear privacy solution. Some might argue that such data doesn’t go with personally identifiable information like complete IP Addresses (semi-anonymized IP Addresses still register), so it should be okay.
But site owners are still sending some sort of data about the user (while the user thought you weren’t) to Google servers before actually anonymizing it, processing it and modeling it.