why woman is not allowed to become Imam (leader)

Femininity is a socially reinforced gender role that has no basis in biology. We have observed time and time again that reinforcing this gender role on women to be sweet, passive, demure, not aggressive, etc has very severe repercussions, especially in cases of rape and violence against women. If women were socialized to be as strong and self sufficient as men, we wouldn't see these problems.