THE DAY THE EARTH STOOD STILL
Remember, if we use nuclear weapons, condescending aliens will come and kill us with weapons even worse than nuclear weapons. I think you might've had to be there, but The Day the Earth Stood Still remains a fine allegory, and a pretty good movie, though it has a little trouble hiding its flabby middle.
1951
Directed by Robert Wise
Written by Edmund H. North (based on the short story "Farewell to the Master" by Harry Bates)
With Michael Rennie (Klaatu), Patricia Neal (Helen Benson), Billy Gray (Bobby Benson), Sam Jaffe (Prof. Jacob Barnhardt), Hugh Marlowe (Tom Stevens), and Lock Martin ft. a fiberglass statue (Gort)
Spoiler alert: severe