In Uglies, people change the natural world in order to suit them better—but that doesn't always work out for the best. Sound familiar? But instead of issues of climate change or genetic engineering (as we face), the ugly/pretty world faces questions around the pretty surgery and the consequences of our genetic engineering (sorry, future guys, that's totally our bad). Tally's society generally leaves the wilderness alone, but they live in a very managed bubble. So while Tally's city is more careful of nature in some ways (using solar power more than oil or wood), the pretty world is a little unnatural and artificial, like a Jersey Shore tan.
In Uglies, everyone needs the city and the wilderness (and not just for camping out). No one can survive without both.
In Uglies, human tampering with nature always leads to disaster, like with the white orchid and the pretty surgery.