I ask this not to argue, but because you seem both pleasant and informed/opinionated and will likely have something useful to say: what as a male hacker am I supposed to be doing about the issue in this thread?
Let's assume what I know's not true for many men - that I am not even slightly coming on to or harassing or creeping on anyone and am very polite to women personally, or abusing position over them, etc. (I used to be treated like some kind of rapist by many women for prosaic things like opening doors or walking down the street, I guess from inherent suspicion of single men - now that I am usually with my wife when I'm outside of work/home, nobody looks at me twice or gives me dirty looks, which is vastly less awkward).
I don't often see situations where women are being harassed these days, so I don't even have scope to act like some kind of gender-police hero. Nor is it always called for, that I can see; I like to reassure or express solidarity with people who are getting treated in a normally dickish way, but usually not in the form of a giant "you are a huge asshole" confrontation, which can be bad for one's career and such, especially when 'the hacker scene is full of assholes.' But if I noticed sexual harassment or implicit threats or something I would already try to make sure something was said.
So what else is there? Should I just admit some kind of privilege and say it's really bad and then I don't have to do anything else, or is there some specific thing I should be doing? Because I can't get a specific reading on what I ought to be doing and sometimes suspect in these conversations that I am just supposed to feel bad and say something submissive, which really isn't satisfying when I have honestly spent my whole adult life consciously trying to be nice and even-handed to women.
Examples off the top of my head: sometimes it may be as simple as noticing that people keep unconsciously interrupting a female coworker for no real reason, so you casually and non-condescendingly form a pause so she can finish talking - or maybe you're helping pick speakers for an event and you've thought of a person who happens to be a woman who would be great to round out the day, but she hasn't submitted a proposal yet or whatever, so you email her to ask if she's interested. And of course you also keep a friendly non-condescending eye out for men who similarly may be getting unfairly ignored or underestimating their own skills, but that kind of subtle social support often already comes naturally for people dealing with their own gender, and it's also somewhat less common for men to be randomly assumed to not know what they're talking about, etc.
In other words, being an active feminist is just generally being a decent human being, to women and to men, but also including a well-informed eye toward the biases left by generations of discrimination.