It is not that simple. Facebook can also customer data from a variety of sources and parties. In addition, it will share measurement data to outside parties. Ev

It is not that simple. Facebook can also customer data from a variety of sources and parties. In addition, it will share measurement data to outside parties. Even if the data shared outside its walls is translated to a new ID, you still end up with an open loop where a user ID is used for targeting, measured, and potentially shared. That user ID is based on their iOS device ID and we know those are unique.