+1: the globally unique identifier that is reused across multiple accounts is an antipattern in my opinion. This is just as bad as reusing passwords. There should be no need for anyone to have to reuse email user id's or phone numbers or credit card numbers. These should be unique per online "relationship", the way your CC chip creates per transaction identifiers. The fake account problem needs to be solved in another way. You simply can't take these GUIDs back once they are leaked and that leaves your only choice to burn them or just accept the risks of having that data leaked all over the net.
joshuamorton|3 years ago