For the life of me I still can't figure out what he wrote that was so offensive. I see people attacking him in general terms, calling him a bigot/sexist/etc, but they never mention anything specific he wrote. Can anyone point to anything specific that is upsetting so many people?
Despite the attempts to provide disclaimers, many of the comments he wrote were explicitly sexist. For example the sections "Personality differences" and "Men's higher drive for status".
Sexism means prejudice related to gender. Prejudice means pre-judging a group. For example the belief that women do not have as high as drive for status can (and previously has been) used as an excuse for promoting men instead of women or a particular man instead of a particular woman.
https://assets.documentcloud.org/documents/3914586/Googles-I...
And other comments. In the context of discussion of things like hiring, promotion and pay, acting on the beliefs he stated has been outlawed (even though unfortunately these biases are still very prevalent). If they do not fire him, the document will be used as evidence in discriminatory lawsuits.
These sexist beliefs are still just as popular as ageist and racist beliefs. Many may be able to find scientific studies that back up their prejudice. There are usually studies backing up just about any view, just due to the nature of science. Regardless of how well accepted or not these studies are, the laws have already been made years before. So if you want these types of prejudicial beliefs to be openly consulted in hiring, promotion, etc. decisions in companies, those laws will need to be changed.