I think you are making a number of poor logical leaps. I have read the memo in its entirety. I have begun the process of reading the citations in their entirety. I am, so far, entirely unconvinced of that he has proven his point about gender bias. I am entirely convinced that he did prove his entire point about the political and moral echo chamber that is Googles Mountain View office. Though he did not do it within the letter. Google helped him by firing him.
Where you've made some poor logical leaps are: there is zero evidence that he shouted out his obviously controversial beliefs to the world. As far as I can tell this memo did not go to the whole world by his doing. It did not go to the entire Google staff by his doing. In fact, for all we know he was asked for his well thought out opinion on Googles diversity training and gave it to the appropriate people who did not respect the fact that he was giving his opinion to a small group and began forwarding it on. You might say I have no proof of this, and you'd be right. But you have no proof that he blasted this to the whole world.
Additionally, he was a number of things in the memo but he was not an unhinged idiot. It reads like someone who was asked for his opinion on the training that was going on and whether there was value in making it mandatory.
I have been asked in professional settings for my opinion on controversial matters. One time I was put into a very troubling position because of my opinion and many people were quite upset. It was uncomfortable for us all. I no longer give my opinion on controversial topics. I keep quiet and do my work and if I disagree with a policy or procedure I find new employment.
I am sure the author of this memo has learned his lesson now. He will shut up. I hope that the world is a better place without his opinion.