You should certainly be able to tell that the person controlling an account is its rightful owner, but it's not obvious to me that you should be able to tell th

You should certainly be able to tell that the person controlling an account is its rightful owner, but it's not obvious to me that you should be able to tell that 2 accounts are controlled by the same owner. If I have 2 accounts, and you can tell that they're both me, doesn't that compromise my privacy?