Don Marquis

In socialism, private property is anathema, and equal distribution of income the first consideration. In capitalism, private property is cardinal, and distribution left to ensue from the play of free contract and selfish interest on that basis, no matter what anomalies it may present.

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.