Yeah, neither the movie nor the book scenarios are actually going to work, for the same reason WW2 didn't create a lasting alliance between the West and the USSR. At best, it'll just create a cooling off period. Then, they build even more powerful weapons to combat the menace, and tension begins to build again over who gets to control those.
The worst case scenario in the comics, Veidt's plan leads to a genocidal war with a totally innocent race of psychic extradimensional squids that wipes out two whole species. The worst case scenario in the movie, World War 3 is fought with bombs powerful enough to kill a god.
Both attempts are so stupid that they transcend the very concept of stupidity and exist in some higher plane of stupid where the Gods of Stupid live and look down upon us lowly mortals. They are the pure quintessence of stupid.
The problem is that every character is partially right in their philosophies, but they take things to such an extreme that none of them could be more wrong. It just so happens that Ozymandias was the only one with real ambition, and thus he could be wrong in a much more spectacular manner.
The Comedian was right in his nihilism but forgot the most important part, that a meaningless life gives one freedom to build meaning. His inability to do so left him to die with nothing, a mere lackey for a dangerous and corrupt government.
Rorschach's black and white view of the world is completely right, but he took it so far that could no longer see the beauty that he set out to protect and was left with nothing but the guilty to slaughter. His mindless pursuit of justice caused him to forget the big picture. He could have inspired millions to shrug off the chains of apathy. Instead he's an ugly mess in the snow.
Ozymandias' obsession with saving the world led him to forget the transitory nature of things, ironic given Lord Byron's poem about his namesake. He sought to change humanity with a single bold act, forgetting that everything is dust in the wind, and all human endeavor is doomed to failure. If he had a bit of Rorschach's razor-edged morality, Manhattans cold distance, Comedian's nihilism, Dan's optimism, or Laurie's humanity he may have chosen a much more sane and more effective route to peace.
Dr. Manhattan, though, is the worst of the bunch in one regard. Though god-like, he's also childish. His apparent inhuman mode of perception often leads him to act without thinking about the consequences of his actions, in spite of being able to view the future. His decision to take sides in the Cold War was the single most irresponsible thing any super being could do.
And Dan and Laurie, though sane, had difficulty looking beyond their own lives. This led to an inability to take action and an inability to prevent the events of the series.