The world of Uglies is separated into the haves and have-nots—those who have had the surgery vs. those who have not (yet). The city even has different areas for the different classes of people, like Uglyville, New Pretty Town, and Crumblyville. (Is it the brain damage that made them give the areas such obvious names?) This is a real extreme form of having a cool table where the cool kids sit in the cafeteria at school. And like different groups in the cafeteria, it can be hard for people of the different classes to interact—so hard that pretty Peris can't even be friend with ugly Tally.
InUglies, class is so much more important than individuality that any interaction between one ugly and one pretty is much like all the other interactions between an ugly and a pretty.
Uglies shows that society is totally artificial, with no relation to the natural world.