<Spoilers follow>
Great read, but I can’t see how anyone would be optimistic about humankind after reading them: a group of humans who think we should be eradicated and invited aliens to do it, or at the least enslave us; collaborators when that eventually happens; and then as you mentioned, MAD, and then a series of bad, emotional decisions, all leading to near extinction.
I just can’t find any optimism in there. And it feels very realistic. I read the entire series during the pandemic, lockdowns, and the poor management of all of it, and the books resonated way too well.