This is one of the few subjects where much of the HN crowd is either experiencing some shared hallucination, or is relying heavily on poor journalism.
There are many comments that classify his memo as anti-diversity (it is pro diversity), and there are many that seem to suggest that the memo claimed women are less suited for these jobs, which again is patently false to anyone who gives it a reasonable and full read.
The injustice here is that this employee was taken to a workshop/seminar, was asked for feedback, which he submitted, and was ignored. His firing only came when his memo was leaked to the public and it became the subject of a media witch hunt.
Had the memo not been public, he would still be working there. This was not a planned firing and there was nothing normal about it. The CEO cancelled his vacation to return to HQ and address the situation caused by the media outcry.
This is a cancerous cultural problem that manifests the worst forms of censorious and authoritarian practices of dictatorial regimes of the past. Diversity at this cost is not worth it. Nothing is worth this kind of environment that is openly hostile and punitive to "wrongthink".
People of various backgrounds are not tokens to be planted into various positions to fulfill some fetish or misguided sense of justice. Under-representation by a specific group or sub group is not sufficient evidence of discrimination or a conspiracy. Deeming programs and opportunities unavailable to people because they don't have the correct biological trait is disgusting, and the ends do not justify the means. To argue that favoring someone because they belong to a special genetic group is rooted in the very "essentialist" thinking that is claimed to be chastised.
There is a better solution to these issues, and at this rate it will never be found. Ironic that some of the world's most innovative people who have no problem bouncing from one design pattern to another, are perfectly content with an approach to a point that criticism of it will get you fired.