I'm skipping basically all the posts to point out my view on this:
I believe in the shadow functions, thus, everyone has all the functions, but underneath each of your conscious functions is another one that works along with or against it, usually without your knowing.
An example is Fe and Fi. Fe seeks harmony around us and can be willign to laugh at something amoral just to make the group feel more close, but beneath it is Fi that sneaks in the feeling of: 'Ummm, wouldn't that make you an amoral person? That would be worse than NOT laughing at it.'
Really, believe what you want, I only use MBTI as a structure of my thoughts. The function order and descriptions are accurate enough for me. I don't need perfect quantitative information. I have crazy Ni and my subconscious.