Do people forget WHY we name people or things? To identify them!!
Simple enough, you would think - but clearly not! It just strikes me as either a real lack of imagination and/or egotism, seeing the child as an extension of you.
When our DS was about 2 or 3, he had several teddies and other anthropomorphic toys to whom he gave his own name: Tim the white bear, Tim the panda, Tim the crab, Tim the penguin, Tim the dinosaur (not his actual name); but you would think that most people who are old enough to be parents would have lived long enough to have heard of a variety of names - or know how to look up lists of them - and be long past that stage where they view the concept of a name as effectively equaling their name, now realising that people have one (or more) of lots of different names, not all the same one.
In fact, even in that example above, I had to state Tim the panda, Tim the crab etc. - which goes to prove the point that, if you don't understand/agree with the concept (and wise practicalities) of giving individual people each a different name (at least within a family), all you're doing is rendering the name pointless. If you're going to end up with Little Sally and Big Sally in one household, you may as well just do away with the 'Sally' and call them 'Little' and 'Big' as if they were their actual names.
With the example above of all the girls in the class being called Mary, you'd probably just end up calling them (Miss) Smith, Brown, Robinson, O'Hara, McDonald etc. to have any hope at all of knowing which one was being referred to - the net result of which is that, with all of these girls having the name Mary, none of them end up being known as Mary, as they just cancel each other out.