He doesn't call for the firing of all women engineers.
He does say that science shows that there are biological differences between genders and thus [hazy logical leap here] we must conclude that these differences are much more significant than any society bias, and therefore it makes biological sense that tech companies would have trouble retaining women engineers and Google should shut down programs that try to counter anti-woman bias.
(Via charts, he suggests that he understands that biological gender differences aren't so big, that there's overlap… but then he goes on to say that Google should shut down anti-bias efforts because biological differences explain why tech companies have trouble retaining women so… it seems he didn't understand the science after all. Oh! Scientists behind the research pointed out his fallacy, too.)
That big scientific study about gender differences in personality? Based on surveys of 17000 people. Number of USA sex-discrimination lawsuits in the USA per year? 24000-29000. If you want to study the way things can go wrong, maybe start there; you won't suffer from small N.