Selection effects: men and women may go into economics for different reasons; for example (as a bit of a caricature); men who want to get obscenely rich study economics to get into business, and women who want to get obscenely rich try to marry into money, and money-grabiness is correlated with pro-free market views.
Another version of this idea that I was going to post: is that conservative women are more likely to become stay-at-home moms and thus liberal women will be overrepresented in all jobs.
That's a much better example than mine and I'm annoyed I didn't think of it first. If that's true, than we should expect proportionally less conservative women in higher education, regardless of major (and the effect should remain once you control for intelligence and/or social class).
Edit: ParagonProtege has provided a link to the original study. Thank you! (^_^)
Link.
Can this be reasonably explained by self-interest? Female and male economists' views are probably coloured by gender solidarity. Government jobs may be more likeable to women than men because of their recorded greater risk aversion. Regardless of the reason government jobs are more important for women than for men. Also in the US where the study was done middle class white women benefit quit a bit from affirmative action in government hiring.
Politics is the mind-killer probably does play a role in explaining the difference.
First two points are somewhat congruent with stereotypes. Anyone who has run into the frequent iSteve commenter "Whiskey" will probably note that the third point indicates women may not hate hate HATE lower and middle class beta males in this case.
This seems plausible since politics is about applause lights after all, the tribes are what matters not the particular shape of their attire. But might value differences still be behind the gender difference? Maybe some failed utopias I recall reading aren't really failed.
Somehow I think this does not include ideological diversity.
No mystery here. (^_^)