> I've tried to think of a good argument against this, but I haven't been able to come up with one.

Why are you spending so much time trying to think of an argument against it? Is it really so hard to consider that women are now leaving programming in droves (particularly in the few years after college), in no small part due to the overwhelming number of men who tell them, day in and day out, that they need to accept the fact that they're "psychologically different" and that's "just reality"?

We encourage women to go into STEM fields and then make them feel like freaks a few years later when they actually try to make a career of it. Especially as they start doing more advanced work in the company, being promoted (and especially in specific IT fields), it becomes much easier to just throw their hands up and say "I'm so done with this shit. Peace." than to be BOTH a great programmer and a constant target/poster child of gender politics (both well-intentioned and otherwise). It's a positive feedback loop.

I tried thinking of a good argument against it because it seems unintuitive. From everything I see, women are ENCOURAGED to go into STEM fields. They are significantly more likely to be hired and promoted when compared to their male counterparts, and get all sorts of support and scholarships.

Are you suggesting there aren't any psychological differences between men and women? Because testosterone has been shown to cause people to be more competitive, assertive, and violent. That's a pretty good indicator of a difference in psychology. We are of course talking about trends here. There are of course individual exceptions to the norm.