I think it is very presumptuous of parents - even parents who hate nicknames and don't refer to their child by them - to condemn everyone else for using them.
My friends
Alexandra and
Benjamin are called
Alexandra and
Benjamin pretty consistently, but if
Alex or
Ben is used in a hurry or in affection by someone else, they don't freak out. I really dislike
Alex, but will occasionally use it to refer to her anyway, because I like her a lot and it is fun to play with her name. As long as it's clear he goes by
Nathan I think your friend is being a bit of a baby.