I'm not sure what you're talking about. I suppose we have different backgrounds.
- I've never heard a single ranking officer in the army or intelligence circle or the judiciary branch ever claim that "it's not clear that secrets are necessary" — you'd be right many don't think it's an evil though. (I've personally interviewed such people among others for research, many times between 2006-2014, and this question was central to some discussions because we were indeed designing political regimes).
- You seem to confuse "secrets", the general idea of hidden information (e.g. a Christmas gift, the location of a weapons repository, the name of a lover) with secrets as a security device (PIN codes, passwords, the layout of a physical key). The former are content, the latter are means to restrict access (meaningless in and of themselves). You seem to argue that the latter can do better with less "remembering" (security practices, FIDO, etc), and sure go for it; but that has nothing to do with the former, actual secret information (content) which you seek to protect by way of such security devices.
- My point was about secrecy as a function of States, well before digital computers even existed, and well after. Modern computing compounds effects but doesn't change the nature of institutions. You'll always need to secure 'dangerous' stuff. I'm not sure how you envision a hostile invading army on your ground, but if you picture that suddenly many red lines appear clearly.
I'll tell you the dirty secret: the less they have an actual enemy to fight, the more they idle, the more "these people who desire secrets" become threats to the wider population — people report that it's such a parallel world view as an insider that focus can get fuzzy, undetermined, self-harming. This is why historically you see many governments pretty much making up enemies: a mundane observer would tell you it's to a classic to unite the population (or your base versus rival groups), but a historical perspective shows it's also to curb the 'natural deviance' of all the shadowy things in a State, to focus them for good when their idling becomes too evil.
None of this black and white. Nothing's fundamentally changed with computers or electronics — it's more game theory, math, and obviously philosophy, psychology, than whatever implementation of a system throughout history.
For another round at not-so-simple-secrecy-management, consider now corporations, first between them, then in interaction with States. You'd think it's all new, unseen before. Go read some account of the 16th century or even before. See how this is just part of human nature. As I tell myself, "deal with it".