So, I'm not an expert, nor can I make any claim to speak on behalf of the deeply under-represented, but there are some things I'd like to comment on in response to Al.
A friend of mine, a woman who works as a programmer in SF and participates in her company's diversity efforts(as well as doing really cool coding for girls outreach as a volunteer!) explained it to me like this: basically, when a women is interviewing for a tech company and sees an office full of dudes, it instantly sets off red flags to her. Most of them have had bad experiences in these environments, and if they've been in the industry for a while, although it's entirely likely that they've accumulated the expertise to improve those conditions, they're just plain tired of putting in the emotional labor for a place like that. So they often make the totally logical choice to pass on such groups, and find places where they can better spend their energy thriving on their own terms.
So that is just one women's perspective in San Francisco, relayed through a dude's retelling, and barely scratches the surface of these issues. But when I heard her story and really unpacked what she was talking about, and connected it to some of the other experiences I've heard about, it was really eye opening. Once you are a big group of dudes with typical tech backgrounds, it is not sufficient to say that you are friendly to diversity. When you make a serious effort to empathize with the BS that women(and other underrepresented groups) have to deal with in this industry it becomes clear that saying, "I have never witnessed any kind of behavior that was hostile towards (not just women)"- the absence of overt hostility!- clearly isn't even close to sufficient!
My takeaway is that if you want to make a qualitative change in representation in tech, you have to abandon your preconceptions, go out and listen to the real experiences of under-represented folks, and make a genuine effort to understand their interactions with this world and place that against knowledge of the systemic issues they face(think of it this way: this process is not too far off from how to do good science or research of any kind, you want to build a better model of the reality).
@Al Mo, if you want to appreciate a fuller picture of reality, I would recommend reading up on the direct experiences of folks dealing daily with systemic discrimination in tech, and try hard to empathize with them. If you take this journey seriously, it will only benefit you. I believe this is a good start, make sure to follow the links:
<https://cate.blog/2014/07/28/the-day-i-leave-the-tech-industry/>