Now, a few things about films of books, before I get into the nitty gritty. I don’t think there’s any story that can’t be told on film, with all deference to Alan Moore and J.D. Salinger. Any claims to the contrary are author’s egotism or control freak natures. Prose, comics, and film are all storytelling mediums, each has strengths and weaknesses, and each have their own structures, conventions and creative vocabularies. Changing mediums is an act of translation, and in any act of translation, some parts translate better than others. The translation lets another person, with all that other person’s sensibilities into the creative process, and so there’s an interpretation that goes on in the process. To be fair, to shoot The Watchmen, you’d need eight hours of movie, and some way of putting in some text-heavy exposition. On the other hand, it does kind of look like Zack Snyder held up a copy of the comic, and told each actor to change their posture until it matched the comic exactly. It would have been long and complete.

I mention this because this interpretation, and this translation is what made Zack Snyder choose bombs over tentacles.
But we should start at the comic, recount the story, and then look at what this all means, and then compare the movie, and see if we can come to some conclusions. In the comic, the machine Dr. Manhattan has been working on transplants a gigantic being from another dimension to downtown Manhattan, and it is the Godzilla of transdimensional tentacle beasts, destroying blocks of the city, and killing thousands, causing great psychological harm to the psychics of the world. The creature immediately dies in the Earth’s atmosphere, leaving us all to wonder what the hell just happened. The net result of John leaving for parts of the galaxy unknown is played the same, but his reasoning is quite different.

The tentacle represents something beyond humanity, something that has caused such great harm, and which may strike again any time anywhere. All comparisons to terrorism aside, it is a unifying terror. Terrorism has failed to do this to us because terrorists are, by and large, humans. This is something we’ve been looking for proof of for millenia, the tentacle is alien. This is first contact, the game changer. In light of this, Dr. Manhattan can stop defending humans, he can leave us to our own means, because our means are now unified against a proven universal problem. We are left knowing little about the wheres and whys of the inexplicable appearance of the tentacles,and exactly what kind of danger it represents, but we do know there is something beyond our meager struggles.

This leads us to Dr. Manhattan. In the comic, this event liberates the man in blue. He has been freed of the burden of being defender of the earth for the cause of American justice and freedom, such as he can provide while Tricky Dick is in power. Dr. Manhattan started off as a scientist, with a sense of curiosity which had been interrupted by his accident. With the appearance of the tentacle, and as abhorrent as the plan was, it did work as we are led to believe, and with his tremendous powers from the accident, Dr. Manhattan could finally do what no other man in history (and for a long time into the future) could do, visit the stars, find other civilizations, and satisfy his curiosity. The mixed ethics of the root cause of his freedom were something he chose to live with as it solved his struggle, the ends had justified the means. Adrian Veidt had taken the ethical step he couldn’t take himself. His job was done.

It should be noted that in the Watchmen, everything is masterfully nuanced, and so Dr. Manhattan’s notion of freedom is probably a conflicted notion in his head. He was isolated by the military and government into doing their dirty work in pursuit of their version of freedom, which as we know in the world of the Watchmen, is anything but free even as far as we understand freedom. At the same time, he had his own notion of freedom that refused to be brainwashed out of him.
In the movie, Adrian Veidt made a device that destroyed blocks of many cities all over the world, and made it obvious that Dr. Manhattan had built them, and was actually the enemy in the end (though not necessarily all along). The weapons were very similar to existing nuclear technology, and were very obviously man-made weapons. What is more significant is that The weapons were obviously made and detonated by Dr. Manhattan. He was framed, and in the process, chased away from the earth.

Now, this is in many ways, the same thing. The world has been united against a common enemy, Dr. Manhattan and the big blue guy is gone. Problem really is, what happens when you show a technology that can vaporize spheres of earth and city, well, all of a sudden it is the new shiny, and everyone wants one, in particular before anybody else, including two-bit third world dictators like North Korea and Iran. In the movie, Adrian Veidt introduces a new arms race to a world one minute from nuclear war. Great job, world’s smartest man. Way to go.