1. From an evolutionary point of view armpit hair is an advertisement that a women is sexually mature. If you can't stand the sight of female armpit hair you may just be a closet paedophile.
2. When you see armpit hair it's hard not to visualise what is going on downstairs. A clean shaven armpit won't get you automatically thinking about muff in the same way, hence it must be less sexy. Of course, if you can't stand the thought of a hairy muff you may just be a closet paedophile. (how good is the word muff by the way - I don't think I've used it since the 90's)
3. Not shaving your armpits has become a bold non-conformist act and I expect bold non-conformists to be better in bed. While getting a sleeve of tattoos has become socially acceptable, natural hair growth is sure to inspire a sharp reaction. I think this is kind of fucked up.
4. A woman with hairy armpits probably isn't too hung up on body image. They are not only going to want to do it with the lights out, the covers up and in a position which doesn't reveal all the body parts they are secretly ashamed of.
5. The role of armpit hair is to hold the sweat which carries the pheromones that makes us attracted to woman. Clever marketing campaigns by Gillete and Rexona have totally killed off this natural mechanism which helps in partner selection. It may just be responsible for every bad relationship you've ever had.
Maybe we need to start a charity month like Movember for women. Pittober or something. It could change everyone's weird attitudes, allow people to rebel in a lazy way and raise money for something important.