You underestimate how well-networked women are. For most of us, before we take a new job, we extensively inquire through those networks about the company, the team, and the manager. And your reputation spreads - if your company is considered a good environment for women, word travels fast. (If it's a bad one, faster)
> you have to work pretty damned hard to get them.
Not really. You have to be a place that treats women with respect, is not socially dysfunctional, and doesn't tolerate harassment. That's it. Word will travel. And given SVs culture, that means a rather small set of companies.
> you'd probably be better off hiring 50 year old straight white men who vote Republican and have been at it since the days of Netscape
In terms of finding people, maybe. In terms of building a team - hell no. Not because any of these attributes are undesirable, but because monoculture is undesirable. (Well, it is for the kind of projects I care about. When it's purely about execution and has a very limited set of customers, it might be less of a problem)