This guy was fired for expressing an opinion about Google policy. It was a political opinion which probably makes it illegal under California employment law. You can't fire someone for a political opinion.
Let's consider this in the terms of employment law the rights of a company to control employee speech. And there is a question of where the line is...
There are some things that clearly would be grounds for dismissal; if he said that women shouldn't be engineers, it would be hard to protect him. He didn't say anything close to that.
He was basically arguing that some Google policies were unfair and counterproductive. Yes, he made an argument that offends some people that as general populations women and men are different (not individually, but considered as a whole). But this is an argument against policy, not against individuals.
Here is the case a lawsuit, particularly under California law
. You can't have an employer take sides in political opinions. An employer can't decide that one opinion is offensive while ignoring other opinions that offend other employees. If you allow political opinions to be expressed, and especially if you provide a forum where political opinions can be expressed, than there is a implicit understanding that there is freedom and security.
I will point out that there have been several scientific studies showing that women (viewed as a group) tend to do better than men at several mental tasks, such as multitasking. No one found these studies particularly offensive, and I am going to bet that no one would be fired from Google for expressing the opinion that women are better at certain tasks than men.
Finally, there is a certain expectation that people can deal with differences of opinion and still work together without anyone getting fired. I feel passionately about Immigration (as anyone here knows) and I speak Spanish. I have a co-worker, a Trump supporter, who wants to build a wall and who has told me that people should speak English in any official capacity.
Guess what. I not only am able to work with this gentleman, I talk to him at lunch, and I would be very upset were he fired.
The left is ruled by the idea that disagreement is hate speech, and that people with wrong ideas must be fired, banned from campuses and in general shut out from public life. This is a dangerous idea.