The best explanation of why he was going to be fired and why that was the right thing to do (that I read) came from Yonatan Zunger, who had recently left a Human Resources position at Google; especially his third point, in the following post on Medium:

https://medium.com/@yonatanzunger/so-about-this-googlers-man...

In many way, it was not an unfamiliar sort of rant for the internet, and I was struck by the author's earnestness and apparent sincerity. It's possible that I make too many allowances for behaviour, and it's possible that I'm easily mislead.

I thought his ideas were not in any way useful, or actionable, even had he been correct;

That the ideas were poorly expressed, and full of such fringe 'truths' as are derived, insincerely, from cherry-picked science in order to be sold as snake-oil cures for the cognitive dissonance of the conservative and vulnerable;

That the expression of these ideas was immensely foolish, especially appearing in the context of what I took to have been his initial intent, an appeal of tolerance of diverse viewpoints at Google.

However, I'm always most disturbed by vitriol online when it's in service of beliefs that I share. It makes me deeply uneasy.