I think a few mutually-reinforcing things are going on, and the narcissistic pattern you describe is a big one. Another is feeling socially unsafe, in a way that's hard for me to summarize, but easier to describe some features of:

• Talk of how women are underrepresented at LW meetups (or whatever) pattern-matches to a moral demand that there be more women at LW meetups, otherwise LWers are bad sexist people. As is often the case with perceived moral demands, this feels threatening and defending oneself by attacking premises and identifying the demander as the Enemy is a really tempting response.
  • The perceived moral demand is seen as vague, which makes it feel more threatening — it feels like one can never know whether or not they're subject to criticism.
    • The OP's first link, for instance, says "no one’s required to inform you that you’re creeping" and "Not a complete instruction set on how not to be a creeper." Even if these are true, saying them in that piece's aggressive tone without indicating that doing something simple gets you a lot of the way ('you don't get cookies for being a decent person') causes me, at least, to feel gut-level fear of doing Something Wrong without knowing it and being blamed. (This fear is easy for me now to ignore, not as easy for everyone.)
• I think people often feel like "sexist" is only ever a term of extreme opprobrium, don't distinguish/feel that other people distinguish between "behaving in a sexist way" and "being sexist", and don't feel like it's possible/other people see it as possible for behaving in a sexist way to be slightly and forgivably bad, so they must defend themselves from arguments that might imply that they're sexist. (This seems easier to illustrate for "racist"; the prototype racist in most(?) people's minds is a Nazi or something equally awful, which makes the claim that it's "racist" to, e.g., be more afraid of a black person on the street at night less thinkable.)
• It is not obviously false that there are biological reasons that women would be less likely to be interested in LW absent any discrimination.
  • This possibility is a good way to claim that one isn't or might not be subject to perceived moral demands, which makes endorsing it more attractive.
  • If this is true and the people making the perceived moral demand wouldn't believe it if it were true (which it's perceived that they certainly wouldn't), then the demand will continue to be there forever even if all actual discrimination is addressed. This feels more threatening.
  • A common response (it feels to me like the most common by far on the Internet as a whole; this isn't necessarily true but the feeling is a relevant data point) to this idea, by the people perceived as making the moral demand, is that it is obviously false and considering the hypothesis makes you a bad sexist person. Independent of anything else, for X to say this about a hypothesis Y thinks might be true is likely to make Y feel threatened and (if Y identifies as a truth-seeker) offended. This leads to polarization and increases Y's identification with the hypothesis.
• This point about 'privilege' language.
• Even if none of this sort of crap is present in a particular discussion, if someone has seen it before, they're likely to pattern-match to it and become more defensive.

All of this is true or not independently of how justified the feeling of unsafety is. Any actual risk is almost always small and the mature thing to do is to feel its smallness, but rolling a saving throw for Not Trying to Please Everyone Unless They're Tagged as an Enemy — at least, that's what not being triggered by this feels like to me — is really hard for some people.