The primary cause of the gender gap is tech is the lack of a gender-balanced candidate pool for tech jobs. If you're a hiring manager posting developer jobs and 80% of the applicants are men, is it sexist that you end up hiring mostly men?
The real sexism problems are happening much earlier in life than when people start looking for jobs. If you want gender balance in tech jobs, we need to get more women into tech-focused college degrees, which means we need to get more girls interested in tech in primary school, which means we need to encourage teaching and parenting in early development that leads to an interest in tech later... etc. But wait, prenatal hormone exposure predicts toy choices in young children [1], so it's not that simple. This is exactly what Damore was trying to get at.
I think we need to split the gender problem in tech into a few different categories and tackle each independently rather than throwing everything in the "tech is sexist" bucket and looking for magic umbrella solutions. At a minimum, there are problems with getting girls interested in tech, keeping girls on an education path that leads to a tech career, eliminating subconscious bias in hiring practices, moving startups away from bro culture, and retaining women in tech when work-life balance becomes more important. All of these are important and require different solutions.