He doesn't use it to essentialize each individual. He's pretty explicit about that, if you read his memo. He's clear about the fact many women are exceptions to these patterns, just as are many men. The point he's making is that, perhaps, in aggregate, these differences explain the relative proportion of women in technical jobs. He isn't saying women shouldn't do technical work. He's not saying Google shouldn't hire women. He's not even saying that the women working at Google don't deserve their jobs, or aren't good at them. Far from it. What he's saying is that efforts to actively recruit women in tech, in an attempt to achieve gender parity may be misguided, because part of the reason for the proportionality difference may be biological. That's the essential point he makes, and whether or not you agree, I think its fairly clear that his point is at least not crazy and worthy of firing.