If possible, I would advise you to go read this post of mine. A good dermatologist with years of experience in dealing with AGA (balding patients) is like a good commander to guide you, bad dermatologist is still like a commander but an enemy commander who picks the side of balding against you in the fight against the AGA. In my earlier forum posts, I mention that I had to deal with arrogant dermatologists myself who did not prescribe me finasteride and caused the loss of 6 crucial months for me. When I look at your post, I feel that you may even be a doppelganger of mine, seriously. I had to argue with doctors too. This is not to say doctors in general are dumb, but some of them definitiely are, and you had come across them unfortunately.
You are not the asshole. The chance of your fertility being impacted by finasteride/dutasteride is low. At 21, you can be prescribed it. Go see a better dermatologist. Also hair transplants are only worth it if you hop on fin/dut, without them it is just buying a few years. Also, without hair at that age your chance of finding a girl to have kids with is nuked the start with. Fin/Dut will help you find a partner to make babies in the first place, few young women would seek out a bald man at his 20s. 