Murray Rothbard

The fact that natural-law theorists derive from the very nature of man a fixed structure of law independent of time and place, or of habit or authority or group norms, makes that law a mighty force for radical change.

Many of Judy Blume's books - which I devoured when I was growing up and where I found characters that were believable because they were a lot like me - caused considerable consternation when they were first published, but now they're widely accepted as an essential part of the children's literary canon.

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.