I really don’t see how Waterwold and The Postman are liberal. /s/
Is the "/s/" for sarcasm or are you sincere? They had a strong libertarian or anarchist streak. But why did the world become watery? Was Waterworld a global-warming or climate change story? And why is Costner's character in the Postman so determined to restore the United States, rather than to enjoy the anarchy?
I won't say that these were liberal stories, but they were ambiguous. The kind of westerns they were based on had the same ambiguity. The marshal who comes to town to enforce the law marks the end of primitive lawlessness, but also the beginning of the road to centralized authority. You could say that they were conservative stories, but liberals might also try to claim them.
Maybe they don't break down easily into liberal or conservative categories, but anything with Mr. Dances With Wolves in it is going to look liberal to a lot of people.
Waterworld- Capitalism destroys earth
The Postman- civil servant rebuilds society