Facebook admitted that they will collect all payment data from all Libra purchases about all people in Full Detail! (Reddit Bitcoin)
Moreover, because the Facebook Payments, Inc. subsidiary processes these transactions, Facebook itself does not have access to any payment credentials information, though it [i.e. Facebook itself] does[!!] collect other information affiliated with a transaction, such as the merchant, the transaction amount, the date and time and the purchased good.
In other words: Facebook will (not only "can" but WILL) completely know about all purchasing details, people will be fully transparent to facebook!
I can't believe that this doesn't cause any outrage. Even the article above is just stating this amongst lots of other text, without any highlighting or special commenting - so it can easily be overseen.
That's why we'll need Bitcoin.