I thought at the very least it was an attempt at a well thought out unpopular opinion that should have at least been met with a productive rebuttal. To fire this guy though, sort of proves his point. You can't speak out against the safe space google is trying to create, without fear. If he's wrong then argue his reasoning. Don't attack his character and silence him.
Google is a for-profit, publicly traded company with millions of investors and thousands of employees. They are not obligated to engage in a public battle of ideas with an employee. They have made their values incredibly clear - if he disagrees with them strongly enough to publish a manifesto, he probably should have already left to find a place where he fit in better. Perhaps Palmer Lucky will hire him.
He didn't make it public, he was advocating for something he thought was for the better. Of course work places can be ruled in any number of ways. I think a lot of peoples perception of Google is that they are pro-intellectualism and encouraged diverse opinions. This shows otherwise. I'm sure he'll be fine, I'm actually not to worried about him. I'm more worried that something like this, something so rooted in good faith and scientific basis, could get someone fired.