And Jor-El's "it is forbidden..." lines came across to me as more "lead by example, not by imposing your powers on the world" which seems like a reasonable sentiment. Maggin's "Must There Be A Superman?" covered a very similar theme.
Well, that's one take on it, but Spiff's is equally valid.
You could make the argument that every time Superman saves someone from a car crash, a hurricane or whatever he's tampering with the course of human events. If he weren't around, those people would die, just as they do in our world without a Superman.
Let's say Superman has a chance to save President Kennedy at Dealy Plaza. Should he do it? Sure, he's Superman. But if he does, he's changed history, hasn't he? That's an obvious example, but who's to say what the "average joe" might mean to the time stream? Maybe the kid Superman saves from a crashing school bus today will be President in 30 years. Maybe the guy he saves from a house fire will go on to murder a man who could have cured cancer.
As far as I'm concerned, either Jor-El is a fool who takes both sides of the argument (help them, but don't make a difference!) or Superman is disobeying his dad every time he performs a super-rescue.
I like Brando as much as the next guy, but this whole "father-son" thing in the films is a bad idea.