For those crying sexism, go take a look at the amount of women in the business, now THAT's what sexism looks like.
Is there anything that prevent a men to work in this field ? I know a guy who did, so I can tell you: Nothing.
If we lack of women in CS it's mostly because women themselves thinks it's not attractive, just like they don't see trucker, or construction worker as attractive jobs. For the same reason teaching, widwifing, etc lack of mens.
IHMO: It's the culture that drive the inbalance in a given field, and the inbalance that create some macho mens, not the other way.
Is it not possible that the cultural imbalance in all of these fields is due to sexism?
That's not every woman, but a very big chunk that I witnessed.
Our school began participating with various groups to secure funds to help encourage women to come into the CS, MIS, or SE programs. I can count on my hands how many additional women joined. Nowhere near enough to call the effort a success. More women chose the classical major choices instead of the various computer fields, even if they didn't show a lowered cost of attendance. Why?
Through it all, I'd have to blame the culture. You don't fix the problem by throwing money at it. You fix it by showing that Penny is just as comfortable around computers as Sheldon is to Theoretical Physics. A field doesn't have to be stylish, and a playing with a computer doesn't have to make you a nerd.
I assure you there's no concerted force working to eschew women from the sciences. If the culture fits and is likened by its followers, I'm sure the numbers will grow to equal measure of the men. If you start from the root, you can fix many of the problems we see today.