Seriously, what is with this trend? Why would anyone care so much about the opinions of the people in the massive corporation they work for? You're there to work – anything else is going to introduce an unnecessary variable.
For this guy in particular, you'd think that at some point whilst writing his 10k+ word screed, he might think "gee, this looks an awful lot like what that Damore guy wrote." In fact, it requires so much naiveté to think that a rage hungry mob of employees he's never met would not immediately dub this a "manifesto," that one must assume that his goal was to start this controversy. Otherwise, why post it? There are plenty of public forums where he could share his views and get the same reaction without also being fired.
Although I likely agree with much of what he wrote (I'm not reading all that), I have no sympathy for anyone who displays such a lack of judgement.
Perhaps the better question is why this internal forum exists at all. It used to be that everyone knew you don't talk politics at the workplace. Now that it's becoming more normalized (with a hefty selection bias for the orthodoxy), people think everyone gives a shit about their opinions. News flash: they don't. Those who pretend to care are only interested because they want to get angry as a form of self-validation of their moral superiority complex. The only way to defeat the mob is to starve them of attention. Eventually they'll hyperventilate on the fumes of their own bullshit, the pendulum will swing back, and we can all move on.
In other words, don't feed the trolls.
I think you missed out on "silence is violence". It's not good enough for the author to keep his mouth shut and his head down. No, he must stand up and repeat what everyone else is repeating or face the same consequences as posting a "10k+ word screed."
If you're going to go down anyway, might as well go down with a bang.
Would you expect your powers to magically dissipate because some people were trying their best to ignore you?
FWIW, I would never discuss anything remotely politicisable on work systems. Vi vs emacs and branching model debates are enough to remind me how vitriolic people can be.