OK, so, obviously, every world in the imperium, to a greater or lesser extent, maintains a unique planetary society.
But is there an 'Imperial Society'? An overarching, interstellar, society that defines the imperium, perhaps providing heroic, moral and societal paragons for the various disparate societies to emulate and aspire to? If so, what is it like? How is it constituted, structured, maintained?
The example i'm thinking of is Ancient Rome. The various Roman provinces all had their local cultures, customs etc. Gaul as different to Numidia. Egypt was different to Iberia, etc. However, they were all Roman; they all adopted Roman culture, religion, materials, building styles...Egyptians and Gauls alike wanted to 'be Roman' (not everyone of course, but many, many did).
So is the Imperium similar?