1) The Blank Slate was published 10 years ago by a psycholinguist (albeit Pinker an AWESOME psycholinguist but that's besides the point). There's been a lot of research since then to muddy the nature/nurture debate.
2) who's even suggesting that we need a 50/50 gender balance? Where are you getting this straw man from? All McClure has asserted is that there should be more women in tech, and given our 9:1 M:F ratio... there's a lot of room to move before we even start to discuss whether 50/50 is an appropriate ratio.
It's not surprising that new and enlightening nature-vs-nurture research has come out in the last 10 years. But I haven't personally come across anything significant with regard to asymmetry in gender-based interests.
Also, I'm not attempting to refute Dave McClure or anyone specific. I never claimed that he claimed we should strive for 50-50 equality, so it's unfair for you to accuse me of a straw man. I'm just making reference to an argument that happened to affect my personal view on the matter. This topic has come up again and again on HN and in tech-related blogs, and I think it's a very common viewpoint that any deviation from a 50-50 distribution is attributable to discrimination.
Regardless, I agree with you that that current ratio is overly-extreme, and that we can do better.