Final answer:
Cities are seen as the 'best cure for our planet's growing pains' due to economies of scale which makes them efficient hubs for economic activities and populations. However, cities can also face diseconomies, which prevent the formation of one massive city and necessitates a balance to maintain their livability.
Step-by-step explanation:
We can say that cities are the "best cure for our planet's growing pains" because they demonstrate economies of scale. When economic activities and populations are concentrated in cities, it leads to more efficient production, as businesses have access to a large pool of customers and workers, which in turn reduces costs and increases productivity. Additionally, cities offer an array of services and attractions that can serve a large number of people. Nonetheless, cities can also experience diseconomies of scale, such as congestion, pollution, and overused facilities, which is why not everyone lives in one gigantic metropolis. Essentially, while cities have their benefits, they also face challenges that need to be balanced to ensure they remain livable.