> The lawyer who wrote this memo argued that Damore's statements would normally be deserving of protection, if they weren't so offensive.
Incorrect; the memo assumed (did not conclude) [0] that Damore’s memo was entirely within the protected purpose, and concluded that even given that assumption, the particular elements within it, for which Google claimed to have fired him, were within the bounds of what Google could fire him for, given their legitimate, pre-existing policy.
A legal decision memo (or a court decision) will often assume a point not because it finds it well supported, but because a dispositive answer to the legal question can be reached without resolving the point on which the assumption is made, and courts and lawyers often prefer to avoid resolving subissues that are unnecessary to resolve in order to resolve the actual question they are posed with.
So it did not argue that Damore’s memo would have been protected but for the identified problematic elements.
[0] key language: “Assuming, arguendo, that the Charging Party’s conduct was concerted and for mutual aid and protection, [...]” (p.3)