You might think it's just one bit of fingerprinting information, but if 99 of 100 users click "accept" and one user clicks "decline", it's suddenly become 6.6 bits. Now combine that with other fingerprinting data and you have uniquely identified the user.

It's the same problem with pages where most users are logged in: the few who aren't are suddenly such a small group that they become identifiable through other means.