I have sympathy for what you're saying here; I think it
would be a totally valid interpretation of the law to say that point 3), however clumsy it may have been, was made in support of point 2), and therefore under protection.
But the way this played out, the board ruled the other way, and I think this is a clear warning to future employees seeking protection under this rule: the NLRB will interpret things as tightly as possible, and be very deferential to employer's internal policies even if they hinder the ability to back up a labor conditions complaint with arguments.
Whether that's okay or not is a political fight, and I see how there's a slippery slope here that could theoretically be used to squash many legitimate labor complaints - if a company imposed rules against making people feel politically uncomfortable, would they be able to fire people for wanting to unionize and backing that up with political arguments that might offend capitalists? I'd be surprised if the board didn't act in that case.
But let's be honest. Damore was trying to score a backdoor win through a legal exception that pretty clearly was not in spirit carved out to protect people in situations like his. That's why I also expect him to fail in any CA civil suit, though I'm less certain about that one, political views are more protected in CA than elsewhere.
Just to be clear, I'm not personally in favor of Damore's firing over this memo, it sounds like Google tends to encourage vigorous internal debate about this sort of thing except when it goes public (as witnessed by the inaction until the memo was leaked and the outcry began). Despite his poor sense of what the response would be, I think he was engaging in good-faith argument, at first, at least, pre-Goolag and that nonsense. From what I hear, people on the left are pretty offensive and vitriolic on internal boards at Google without being disciplined [0], so I'd have loved to see management manage the situation and internally broker some peace between the offended parties rather than turn the thing into a classic alt-right recruiting talk-point by firing him. But I'm very much in favor of a company's right to fire anyone, for almost any reason, and I'm glad that was not interfered with here.
[0] Edit: from the memorandum, a Google employee was reprimanded for responding harshly to Damore over email: '“You’re a misogynist and a terrible human. I will
keep hounding you until one of us is fired. F[*] you.” The employee was issued a
final warning for sending this email. '