Who watches the Watchmen?

[Shepherd]

I do believe that was part of the point of it. It took a long, hard look at things that comics before that point hadn't dwelled upon regarding the realism of their worlds.

Thats part of what deconstruction really means, IMO.  Break a story down to its base components and take a hard look at all of them.
On the subject of book vs movie...  there is one big hole in the 'reconstructed plot' of Veidt...  Framing Manhattan as the villian requires Manhattan to maintain a presence of some sort so that people continue to fear him/his works in order to remain banded together against him.  In this reguard the book's mysterious extradimensional entities worked better IMO

Another flaw, as pointed out by a fic based on the movie, is that Veidt's plan involved hitting millions of people with the same type of energy that created Dr. Manhattan in the first place.
  
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"Anyone can be a winner if their definition of victory is flexible enough." - The DM of the Rings XXXV