The main difference between the societies of Waknuk and the Fringes is the society’s organizational structure.  Waknuk is an agrarian theocracy, and there is generally anarchy in the Fringes.  Sealand is an advanced society with modern technology and telepathy.

Waknuk is small and made up of farms.  Religion rules everything, which is why I called it a theocracy.  Apparently the “Right Wing Church Party” rules everything (ch 6).

We know a little bit about Waknuk from David’s description to Sophie, the little girl with 6 toes who is an outcast in his society.

The civilized part of it -- of which Waknuk was only a small district -- was called Labrador. …Round most of Labrador there was a great deal of water called the sea, which was important on account of fish.  (ch 4)

Yet the most distinguishing feature of Waknuk is that they have decided that everyone and everything must be a certain way, and any deviation is destroyed.  When people are expelled from Waknuk for having some kind of mutation, they go to the Fringes (the outer areas), a place of “dubious safety” (ch 6).

David has to run away to the Fringes because he is telepathic.  He and his group discover his uncle’s compound, and it is very different.  It is even less advanced than Waknuk, seeming to confirm its reputation as “a lewd chaos” (ch 8).  David describes the village as a “conglomeration of hutches and shacks” (ch 14).  Apparently the people on the Fringes sometimes raid Waknuk (ch 9).  Most of them are deeply resentful at having been kicked out, and they seem to be run by warlords like David’s uncle rather than one legitimate government.

In Sealand, people are more like David and his friends.

'Sealand must be a funny place. Everybody there can make think-pictures -- well, nearly everybody -- and nobody wants to hurt anybody for doing it.' (ch 13)

Apparently being telepathic is valuable in Sealand, and people cultivate the talent.  The Sealanders consider Waknuk primitive and the Fringes as savages.  Sealanders consider themselves “New People” (ch 14).  Sealanders consider change a part of the natural process, a belief completely contrary to those of Waknuk.

[Your father and his kind … have become history without being aware of it. They are determined still that there is a final form to defend: soon they will attain the stability they strive for, in the only form it is granted -- a place among the fossils. . . . (ch 16)

Of the three societies, none closely resemble ours.  Each of them is a vision of a post-apocalyptic world.  We either descend into anarchy, go back to the 18th century, or evolve into a more sophisticated people.

The social commentary here is clear.  People who try too desperately to prevent change will end up getting destroyed by their own stubbornness.  The only kind of survival is in progress.