" the libertarian would be free to say that if the stories of our liberty are just fictions, those who like those stories should be allowed to try them out, regardless of the consequences."

I don't see how this follows. I use "fiction" in the sense of a legal fiction, not something concocted but rather a handle on a squishier concept. For example, I believe that free speech is essential to a successful democracy because it is how electors learn what their fellow citizens care about. Because I want to know what you think, YOU get the "right" to say it. That right is a "fiction." You don't have it because you're a voter; you have it because I am a voter, but you are the one most likely to know that your speech is being suppressed. So, as a practical matter, the "fiction" of your "right" to speak is created. But nothing about its fictitiousness makes it subject to challenge as policy.

I agree that the question is how society should be organized, but I don't understand the ideas of honorable or aesthetically great "fictions." I would start with Eleanor Ostrom's work on management of the commons and then try to identify the extent to which a society presents commons and consider the best way for those commons, and only those commons, to be managed.