The gap between what we are and what we can be is also the space in which utopias are conceived. Utopian literature, at its best, may document in detail our struggle with personal and societal failure. While often constructed in worlds of excess and plenitude, utopias are a reaction to the deficits and precariousness of existence; they are the best expression of what we lack most. Thomas More’s book is not so much about some imaginary island, but about the England of his time. Utopias may look like celebrations of human perfection, but read in reverse they are just spectacular admissions of failure, imperfection and embarrassment.
... it is crucial that we keep dreaming and weaving utopias. If it weren’t for some dreamers, we would live in a much uglier world today. But above all, without dreams and utopias we would dry out as a species.
I'm big on the idea of the space we create with our imaginations as a kind of sandbox — in both the sense of "playpen" and the sense of "protected code zone" — where we can try out different stuff and see how they fly. Most of the time, though, such thought experiements seem to be work best when they deal with how things fall apart. We read and think about our dystopias far more often than our utopias.
Some of that might well be rooted in how fiction is about conflict and punctuated equilibriums. Even though the drama of something like Walden Two is in whether or not the narrator will decide to favor the micromanaged commune over the real world, Brave New World seems to be read far more widely and enthusiastically — to say nothing of 1984 or WE.
But I think there's a slightly deeper reason dystopia is the necessary thought experiment that we keep performing again and again. Karl Popper's notion of science was that any scientific insight depended on falsification to be useful: if you can't figure out how to disprove something, then you have no way of really testing it. Likewise, the dystopias we dream up are the falsification experiments we run against our dreams of the future: How badly could this get screwed up? People being what they are, the answer is usually Very badly.