Lot's of missing the point.
It isn't just that Dr. Manhattan wiped out a few cities and we all hate him and that will unite the planet - though there is that too, at least in the short term.
It's that in the new version, God is watching. The fear of that will last a lot longer than the initial hate.
The entire concept of the movie is that we as humans don't have enough wisdom to use our toys responsibly.
It's a pretty cynical outlook on humanity, and one that has a kernel of truth in it, though overall I don't share the outlook.
But yes, I think certainly for the next few decades the concept that a near omnipotent being would punish us for drifting too near nuclear war would have real repercussions on the world stage.
And that might be enough to bring us back from the brink and exam what it is we were actually doing.
Of course, the funny thing is that the Nixon caricature and Veidt ultimately had the same answer, they just pursued it different ways. And Veidt, being smarter, answer was more successful - if no less inhumane.
A sociological examination of what happened after that would have been interesting. Mahattan gets portrayed as an old testament God.
But the ideas of how you create a weapon to kill said God - there's no indication that such a thing can be done. Veidt certainly couldn't do it, and he's Einstein and Hawking and Descartes all rolled into one.
Though it does raise an interesting point - would humanity risk destroying itself in order to restore its perception of freedom against a God that granted it peace?
Moore's take seems to be only those like Rohrschach would actually do it - politicians as a rule don't have that maniacial commitment to an ideology that leads to that end.
Hell of a movie, and while I don't agree with Moore's take on Veidt (you think the smartest man in the world would have come up with something better) it does pose some really interesting questions about human nature.