What escapes this whole shebang is the fact that his post went Viral inside google. Would he have been fired if it didn't?
Perhaps not. But I don't see the fact that he wrote it as the proximal cause for his firing. I suspect it's the fact that his PR event caused by the memo makes it harder for the company to hire women and to draw a clear distinction between Google company culture and, say, Uber company culture.
Or, put another way, the PR makes it harder for Google to defend itself in lawsuits from current or former female employees alleging discrimination. Would failure to discharge Damore itself constitute grounds for a complaint of a hostile work environment?
There is some heavy legal machinery firing underneath the covers here, forcing Google's hand.