Men and Women bring different things to the table. What makes a well rounded child is the different views and examples surrounding him/her.
I identify with my mother not my father. Not saying that my father was a bad model but, that I am a women and I identify with another women. My point being that, scouting should be of a diversified bunch. Even though I identify with my own gender I do use my fathers exapmles for choosing a mate or other males in my life. So yes you do need both men and women in such organizations that involve children. Not all children will be blessed with good role mode