I mean, really, the world's smartest man, trying to change the world and save it from its own demise, hatches a plot that will bring world peace. The brain/squid thing blows up, killing millions. The world thinks that they encountered an alien life form and are going to be intent on learning more about it. As long as they are working together on this, World War III will be avoided. And when it seems like Adrian Veidt has essentially become the other real-life god, he is soon questioning the morality of his own plan. I mean, he killed millions to save billions. A neccessary price... or is it?
I think that I initially hated the ending because I wasn't expecting it. It seemed too outlandish to fit in with the rest of the novel. But now that I think of it, I probably should have expected an ending like Watchmen's. There's the whole masked heroes deal, for one thing....
I also think that I didn't like the ending because I never quite understood it well enough. I didn't think about it enough, or pay attention enough, or whatever. The point is, I'm looking at it differently now, and I like Watchmen again.
Let me cut to the chase: I changed my mind when I realized that there wasn't really a better way to end Watchmen. I found something on the internet which really brought out the side of the argument that I needed.
I eventually decided with the brain/squid thing, people would possibly think it was an alien, wonder where it was from, how it got to Earth, why it blew up, etc etc. In other words, everyone would be so preoccupied with this... thing that they wouldn't care to wage war on each other. It makes Veidt look like a genius for pulling off the whole thing. In the Watchmen movie, Veidt just looked like a puppeteer more than anything, with how he made Dr. Manhattan cause those massive explosions.
I did some investigating of my own and found some scripts for the Watchmen movie that never made it. One ending had a scheming Veidt use some sort of time portal thing that he would use to kill Dr. Manhattan before he became Dr. Manhattan. In another script, Veidt fired a beam of radiation at Earth. Obviously, neither of the endings were any good.
And nothing that I could think of worked, so there we go. The giant squid is needed. End of rant.
