I actually thought the document was reasonably well written, using language that was not confrontational or aggressive, and providing some sources. So, from a superficial view, it looks well-thought, scientific and non-malicious. This is why I presume it gathered a lot of supporters.

The problem is when you actually look at the message and the information given. Some of his arguments are just wrong. And doing what he did was naive.

Biological differences between men and women are completely irrelevant to the very few highly competitive folks in the tech industry and more precisely in Google. Especially considering the huge chunk of the world who is illiterate, we simply cannot have any clue how biology is actually affecting us and how it plays with all the other variables in the game (such as being socialised for specific tasks when growing up, or just finding the workplace hostile). On the contrary, he shows lack of basic knowledge on history of computer science. Since women used to be the majority in the field some decades ago, there is no way evolution / innate difference could have worked its way in this fraction of time. It also makes me question what are his thoughts on people who are disabled and work for Google, for example? This discussion not only is not productive but puts him under a very bad light.

Secondly, he seems not to understand the role of Software Engineering really well. He argues that women are more focused on people and therefore don't feel attracted to high pressure rational fields, but choses to ignore how important people are to the career as a Software Engineer? It seems he is very attached to the idea that programmers are isolated nerds on a basement, which does not reflect at all the actual reality of successful people in the field.

Last but not least, as I said, he was very naive. He writes this 10 page thing about how women are maybe not interested in CS for these many reasons and criticises Google's approach to diversity, with the message that maybe it's not worth it, proposing we use even less empathy. Google has these programs after counselling with experts in the field, which he certainly is not. He says Google is an echo chamber and complains they are not listening. What he doesn't realise, however, is that by circulating that document he is shitting on the head of many of his female co-workers with his wrong arguments, and shitting on the head of whoever are the experts responsible for these diversity programs. And even if he was right, it would still be a bad idea. You don't circulate a document arguing that a certain gender may be in general unfit for the job, and expect people of said gender to be cool with it, even if you claim the people working with you are exceptions. Replace "women" with different groups and how his piece really hit me may be understood better. I don't want to hear "women are bad at math, irrational etc. but you are different, you are cool". Imagine saying to my happily married gay friends that gays are promiscuous but they are ok? He really did not think through how this would sit on people's ears. I felt really disrespected and I don't even work in Google, imagine the women who felt the same but actually had to work with him? It's a massive disruption to the workplace. Google had no alternative but to fire him. A bunch of people would quit if they didn't. I know I would. So Google made the right choice for the company. They put a lot of effort into hiring the best people. Losing one of them is better than losing credibility and losing many.

I'm not saying he's a horrible person and deserves to be fired. I'm saying he is wrong and he made a terrible mistake that offended many people and led things to where they are now at no one's fault but his own. Everything related to this document is really unfortunate, to him and to everyone else involved. It decreased morale of women at his workplace, it got him fired. It also got a bunch of alt-right nazis spreading hate about women using his document as a base, which I'm certain was not his intention.