well, I suppose it's interesting that this thread devolved into a discussion of hairy armpits.

Why is it okay for men to have them but not women?

I consider myself very feminine. I shave my legs but not my underarms. Personal preferemce. It is certainly looked down on by many American men but also I have met a great many who find it very sexy.
As far as I know, the majority of European women do not shave their armpits either.
Different strokes for different folks. I think women who shave too much of their body hair off are pretty gross to look at, personally...