Putting emotional reactions aside for a moment, I think the real point is that unbiased behavior is quite difficult to achieve and requires discipline. If you're not doing anything systematic to root out bias and just relying on good intentions, it won't be enough. Yes, having a variety of interviewers helps somewhat, but people can be biased in similar ways - it is possible for women to be unconsciously biased against other women, for example.

The solution isn't bias in the other direction, but to look for ways to remove the bias. This is why in science we have things like double-blind studies, for example. In music, doing auditions behind a screen seems to have been effective.

Putting systematic measures in place against bias also tends to help with self-selection, since it assures applicants that they have a fair shot. I believe that's what the original poster was asking for. I don't know what the best solution is for something like Y Combinator, but it seems worth giving it some thought. Of course, it's not going to be so easy as performing music behind a screen.

The percentages you cite show this is a problem in many industries. I doubt that 50% is achievable, but I also don't think it's helpful to either say "these people are sexist" or "yeah, but everyone does it." Those are both examples of moralistic thinking. The solution is to move beyond that sort of thing and treat this as a problem to be solved.