Yeah, I agree with those points about the ending -- or, well, I'm not sure that we're *supposed* to think the scheme wouldn't work, in the book, but that the way to critique it is not to try and make the evil scheme better but to give hints that it wouldn't work. I honestly have a lot easier time believing that the New World Order falls apart of its own accord than that Rorschach's diary makes any difference to anyone.

I think the new ending is *marginally* more plausible than the alien scheme (though it still has the problem of Dr. Manhattan being very publicly an American weapon) but I feel like the new ending doesn't really solve the 'hmm, would that work?' problem and creates new ones. (Like, Jon blithely handed over a doomsday machine to his good friend Adrian who is totally sane and could not possibly have a sinister use for it -- I suppose I could believe that about Jon but I need more convincing than the movie gave me.