Why do we judge women so harshly?

I like Nicholas Kristof's hypothesis, articulated in his opinion piece, "When Women Rule" in today's NYT. Well, at least it's an appealing one from a woman's point of view. Kristof briefly reviews successful women rulers in history (Queen Hatshepsut, Catherine the Great of Russia, Elizabeth I of England, Isabella of Castile, and Maria Theresa of Austria among them) and speculates about why these female monarchs were unusually successful in comparison to women leaders in democracies. He writes:

In monarchies, women who rose to the top dealt mostly with a narrow elite, so they could prove themselves and get on with governing. But in democracies in the television age, female leaders also have to navigate public prejudices — and these make democratic politics far more challenging for a woman than for a man.

Hmmm. The column provides interesting empirical evidence . . . and food for thought about why it's so hard for women to get ahead.