Since it's observable with a telescope, the existence of the object is not the secret, but the information it provides access to, and the motives for using this stategic platform, remain speculative. There's nothing else like it that we know of, that any branch of the military, or that any paramilitary defense organization will admit to, and yes, that is being used as a form of propaganda.

Science and the military do intersect for some interesting infotainment though, even if the implicit misanthropy of it all is somewhat off-putting.

It's been posted here repeatedly because sometimes submissions don't get traction for whatever reason. It's newsworthy insofar as it's been in space for ~2 years and just returned, which is a long mission for a reusable. I don't think there's anything wrong with being interested in military technology.

Are you referring to this, maybe? http://paulgraham.com/submarine.html