I don't see what you'd get out of calling someone who looks and acts and lives as a woman a he. It's different than someone you've always known as a man asking you to call them a woman. In this case it's not just a preferred pronoun, but a pronoun that every other member of society is using. Is a boat a woman? No, a boat isn't a woman and has no resemblance to one. But a boat is still a she, because society has deemed boats shes.Define the word 'friend'.
You also should understand that you are among a community of persons that see sex and gender as a unified binary concept. And as far as your responses concern me, let me propose this example.
Let us say that I have a friend by the name of Jane that I have known for 20 years. This person does not exist, but let us imagine. She is an above-average female, in that she dresses, speaks, acts, and comports herself in a way that a woman should. In fact, you may say that she is a very beautiful woman. She is a woman that has spent much time with me in a continent, platonic manner, and so I know her very well. However, it comes to my attention one day while at her home, that I happen to walk in on her undressing by accident, and I see that she has male genitalia. Further conversation with her disposes me to the fact that she is, in fact, genetically male, and that she has taken hormone replacement therapy since her early teens.
It would be my duty to start calling 'her' by pronouns naturally ordered to his God-given sex. Pronouns have no place in being kind. To be kind is to be witness to the truth. Now, Jane can reserve his name, certainly, because a name is used sparingly. When we reference people, pronouns are almost always used when the subject is understood, and so the true information about Jane's sex comes out through pronoun usage.
I would not call Jane by his natural pronouns in order to spite him. On the contrary, Jane is very welcome to remain my friend. I would assume that Jane is perhaps a very kind and tolerable person if I have been friends with him for 20 years. If Jane would end our friendship because of a change in pronoun usage, then perhaps Jane was never a friend to begin with.
Again, I want you to define the word 'friend'.