I wonder if perhaps what mjg is saying is that it is generally the case that those with HFA tendencies who are HF-enough / not-so-far-down-the-scale that they can be productively involved in collaberative software development are by definition sufficiently intelligent and self-aware to be able to modulate their online behaviour.
They might not do brilliantly in face-to-face social settings, but they can almost certainly learn to apply to some rules to improve the way they communicate online. (Note that these rules can include things like appropriateness, etc.. which could go to addressing the more specific perceived problem of sexism, in addition to generally improving the state of communication in free software - the sometimes aggressive/unfriendly/unappealing aspect of which I personally suspect is at least a co-contributing factor in the gender imbalance).
In order to form and apply any such rules, HFAs would need /more/ in the way explicit feedback, rather than just accepting inappropriate behaviour from them. Further, the "form" part can be bootstrapped somewhat.