I couldn't disagree more, and forgive me for saying, but I believe this to be an incredibly shallow summation of what is an amazingly deep and moving piece of art and perspective from a historic time in our (US) nation (the Cold War).
I believe the ultimate theme of Watchmen is this:
"In an irrational world, only the irrational becomes rational."
This theme is pervasive throughout the novel:
_ Regular people donning masks to fight crime at little personal gain and great personal expense.
_ Horrific and violent crimes disregarded as minor indiscretions of a time past.
_ An all-powerful god, resigned to do nothing due to the ineffectiveness of doing anything.
This theme climaxes when Ozymandius, the universally recognized "most intelligent man in the world," (translated, "most rational") illustrates exactly this point when in order to save a world on the brink of irrational self-destruction, theatrically stages an alien invasion, something which simultaneously changes nothing, yet everything, in order to save it.
Even the all powerful god recognizes this seemingly illogical and horrific solution as the ultimate most perfectly rational means to save an irrational world from itself.
In the end, the story's hero, Rorschach, the consistent (and author appointed) voice of reason amidst a delusional world, is rendered ineffective and unable to make a difference, an impediment on the path to salvation to be destroyed by its god, Dr Manhattan.
Let that last point sink in for a moment, and you'll understand the implications of this theme; it's the final scene of an epic novel:
__the world's last rational man is an obstruction to the survival of an irrational world.__
The theme itself is startling in its simplicity, and the impact of watching its very real once impactful characters, heroes and anti-heroes, struggling to come to grips with their irrelevance in an irrational world can be moving and profound in its implications.
Watchmen is a postmodern thesis. Whether you share in the postmodern sentiment, understanding the context is incredibly rewarding, emotional and thought provoking.
Tragically, the movie's creators did not understand this and lost the the whole point and very soul of the novel, transforming the antihero, Ozymandius, into a lunatic and villain. Understandably, this is likely the source of your misunderstanding. Ironically, the replacement of the antihero with a villain could itself be construed as an unintended commentary on the persistence of our world's delusions.
The theme itself is metaphorically mirrored internally within the "Tales of the Black Freighter" story. The Black Freighter is a tale of a hero's lamentable decent into darkness as he loses his grip on reality to become the villain he was running from by ultimately in ignorance murdering his last tie to his world (the light), his wife. It's a commentary on the world of Watchmen itself (the world in which the heroes exist, not the heroes themselves), and the manner in which they metaphorically murdered their once heroes and only hope of salvation to descend into irrational darkness. Make no mistake too, the salvation brought about by Ozymandius is no salvation, but instead the coup de grace of a once rational world's beyond salvation ultimate embracement of the darkness, the conclusion of the novel.
The greatest tragedy of all though, is the spiritual death of its heroes. Alan Moore sums it up well with his inversion of the famous satirical quote, modernly taken as a criticism against political corruption, "Quis custodiet ipsos custodes?" ("Who watches the watchmen?"):
"'They're watching out for us, who's watching out for them?'"[1]
In an irrational world, only the irrational is rational, and the core of who we are becomes backwards and called into question. Do we define ourselves by the changing world around us and betray who we once were, forcing us to withdrawal into ourselves, Nite Owl, or do we "Rage, rage against the dying of the light" to our ultimate destruction, Rorschach?
Or do we embrace the darkness, as Ozymandius did, or as so poignantly put by Harvey Dent / Two-Face in The Dark Knight:
"You either die a hero or you live long enough to see yourself become the villain."
____ Update
This post led me to read a little more on Moore's own interpretation of his work, and while Alan intention is for us to question the need for heroes, and a call to personal responsibility, specifically anti-Reagan, I don't find this to be inconsistent with my analysis. I would add this:
My romanticism of the heroes may at first blush seem inconsistent with Moore's intent. However, as you can see in my conclusion, I point out that the heroes themselves become corrupted by their own roles in a world that rejects them. Moore himself is equally inconsistent in his own analysis of his work, claiming it to be a criticism of the Reagans ("invulnerable" "heroes") of the worlds that lead us to the brink of madness, yet it's the world that rejects the heroes in its madness that drives itself to brink of extinction.
Moore said writing Watchmen allowed him "to purge himself of his nostalgia for superheroes." Something I feel is best illustrated in the inconsistencies between his own motivations and my analysis.
[1] http://www.tcj.com/a-portal-to-another-dimension-alan-moore-...