I'll add in what you failed to mention - that the movie is a poor rewrite of a 1959 Hugo award science fiction by the same name, by Robert Heinlein. Wiki says that the script came from an unrelated script, but I guess the parrelels were too similar and they had to buy the book title rights. The reflection here is how often things get "rewritten" and purloined from elsewhere then passed on as something unique.

My two cents? read the book.