Universal messages are the comfort food of film language. They are the reason you will do better with a story about love fixing all your problems than a bully beating you to death for standing up to them.
A lot of writers discuss this issue as a moral quandary about selling out.
It isn’t.
Casablanca succeeds on every level. The universal message of Casablanca is the problems of two people don’t amount to a hill of beans. Love is great, but there’s more at stake here than some oxytocin and dopamine. That’s not a fuzzy little feel-good sellout of an idea. Sacrifice is ennobling.
A universal message basically finds a way to say “We’re going to be okay,” and it is as universal as the number of people who agree with your premise of what okay is.