Of course, but the question is what that unique identifier denotes.
An IP address tells people who you are, where you are, and what you do.
A unique identifier ('+18El1iZRFCIiqRpfw4dJR8mXjJn2UxPrjwoRNpjSWg=' for instance) tells what you do without the who and where [1].
It's even possible advertisers could still target users based upon these identifiers, just without the background knowledge that makes these sorts of things privacy issues.
[1] I'll admit, it could be argued that the what can determine the who and where
An IP address tells people who you are, where you are, and what you do.
A unique identifier ('+18El1iZRFCIiqRpfw4dJR8mXjJn2UxPrjwoRNpjSWg=' for instance) tells what you do without the who and where [1].
It's even possible advertisers could still target users based upon these identifiers, just without the background knowledge that makes these sorts of things privacy issues.
[1] I'll admit, it could be argued that the what can determine the who and where