I liked the juxtaposition of Ish's community against the suburbs you travel through just after the sewers.

Ish's sewers were populated by people who believed in their fellow man, who worked together to build some semblance of a working community using the scraps in the sewers because Ish was willing to take a chance on them. The notes left lying around make it sound like things were pretty good before everyone got infected, they even had working water collection systems and classrooms. They protected themselves, but were clearly open to taking in other survivors as well.

The people in the suburbs on the other hand, perhaps even going back to the beginning of the outbreak, were isolationist; we can see this from the messages like "Will Shoot on Sight" painted on the walls of the houses. This group eventually evolved into the Hunters, going so far as to trap and kill "tourists". And for what? The few supplies they had if they even had anything at all?

Yet despite Ish's group being seemingly better prepared for the apocalypse what with their sustainable living, it's the hunters who wound up surviving (until Joel rolls up and murders them all anyway). Despite the strength of community that we all want to believe in, it's the monsters of the world, the ones who condoned and even encouraged murder from the early days after the military abandoned the zone, who became the "last of us"

I think it's pretty clear that the sewer/suburb contrast was set up directly to make us question whether whatever's left of humanity is worth saving in the first place and to drive home the idea that selflessness is not the way to survive in TLOU's world, ultimately culminating in Joel's selfish decision to save Ellie from the Fireflies.