I do think the Prime Directive is one of Star Trek's most foresighted inventions and probably universally applicable.
And one of the best episodes ever is still TNG's "First Contact" that says it all, IMHO.
What would happen, if there actually was a global close encounter of the third kind in our lifetime?
Maybe half the people of our planet would adopt their ethics and guiding principles while the other half would simply reject it. Since we are right now plunging back into the Dark Ages with religious fanatism and murder becoming ever increasing, that's just what we can use right now to insure the demise of the human race.
In simpler language: Benevolent aliens would cherish the Prime Directive on our behalf, evil ones would come and say "hello"...