This makes an excellent point, and the same could be said of the junior moderation team - the HN readers who up/downvote comments.

A practical solution: The mods might ask people in underrepresented minorities for some honest, frank perceptive and feedback. Stop guessing and trying, and get some real knowledge. Look at particular threads (on sexism, etc.) and talk about how welcoming HN is to them and why. IME, there is no substitute for a lifetime of personal experience with these issues; most people without that experience - including myself - are surprised when they hear the realities and details.

You can identify who is underrepresented and who might feel unwelcome by what groups are referred to as "they". For example, in discussions of sexism women are often discussed in the third person - a good sign of who is the excluded group. If you think about it, those discussions should be led by the people who have experience with the issue, just like Java devs (hopefully) lead the Java discussion. This discussion, right here and right now, should have those voices - it's right in front of our eyes.

I'll add that religious prejudice against Muslims is particularly overlooked. If I were Muslim, I would not feel welcome here at all. As a practical test, substitute in 'Jews/Jewish/Judiasm' for 'Muslims/Islamic/Islam' (to pick a religious minority against which prejudice is rejected, as it should be for all) and evaluate the statement. I've seen many that unambiguously fail.