It was a way to quickly implement secret identities without rewriting the game. 15 years ago "goblins is bad" was enough. DF was a completely different game. Now it's not enough. Hence, society arc rewrite, planned after Mythgen.
It is an example of how the design strategy is fundamentally flawed. Things do not fit into tidy 'arcs' because a computer game, like the real-world is not organised by "themes". Elements of one thing do not organised with other things because they are similar, they are linked together on an entirely different basis. So to develop a game in terms of thematic arcs does not work because mechanics that are part of one "theme" typically are closely related to mechanics that are part of another "theme".
The organisation of the basic code for sites, requires an understanding of the security status of the different parts of the site. It does not require a fully fledged social statuses to exist beyond the rudimentary outsider-insider distinction, the adventurer in most cases being the former. Even though the society is already advanced enough to create several security grades for site areas, we are still using a blanket system based upon pure ethical values which results in insane, genocidal consequences in practice because the society arc is not yet come.
Yet we have already have enough social distinctions in the game for a proper implementation of security zones to exist. The present situation sucks up resources at a crazy rate and exists because of the flawed way the sites were originally defined without regard for security. What we *need* people to do is keep strange people away from prisoners and valuables, not have them have to stay out of the whole site to accomplish this.