In her column the other day, Peggy Noonan wrote about Oppenheimer:
I thought “Oppenheimer” would be more of a warning, and I wanted it to be because I think the world needs one. In fairness, the first two hours of the film signal a kind of warning, with a building sense of dread, but it dissipates in the last hour, which gets lost in a dense subplot. I wanted the director, Christopher Nolan, to be an artist picking up unseen vibrations in the air and sensing what most needed to be said.
I think, though, that there is plenty of warning in the movie. Oppenheimer is haunted by visions of the victims of Hiroshima and of the coming age of nuclear-armed ICBMs; he wants to stop the arms race and fears the H-bomb; and — without spoiling anything by being more specific — Nolan makes sure to underline a monitory note in a key subplot.
Anything more than this, in my view, would have ruined the artistry of the movie by being too didactic.