Joan Didion

To make an omelette, you need not only those broken eggs but someone 'oppressed' to beat them: every revolutionist is presumed to understand that, and also every woman, which either does or does not make 51 percent of the population of the United States a potentially revolutionary class.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.