One of the graphic novel's subplots had to do with the perceived instability of the MAD doctrine, which kept us and the Soviets from blowing each other to emcee-squared by guaranteeing that neither side would survive no matter who launched the ballistic missiles and bombers first. This instability was a popular line of thought in the New Left*, and spawned quite a few stories where the US and USSR teamed up against an alien menace, or are blackmailed into laying down their nuclear arms. Watchmen is one of those, and it sticks in Collier's craw.
I say he needs to grow up and learn to appreciate period pieces for what they are, or avoid them along with the consequent butthurt. I didn't see the movie as a repudiation of 300 in any way, and I think when you start seeing things in that light you need to step away from the computer, switch from Coke or coffee to 7-Up, and chill the fuck out. It is worth emphasizing here that the actual hero of Watchmen is not Ozymandias/Veidt or Dr. Manhattan, but Rorschach, the uncompromising vigilante whose "dead man switch" of a journal left at The New Frontiersman may unravel Veidt's plans despite its author's seemingly pointless death in the Antarctic waste.
It is what it is. Moore may have intended Watchmen as a slam on Ronald Reagan, who stupidly thought we could win the Cold War (see what I did there?) but if so, it's one obscured by the deconstruction of the superhero/masked vigilante trope and the parallel history presumably invoked when Nixon runs in place of Goldwater in 1964 and unleashes Dr. Manhattan on the recalcitrant Viet Cong and their North Vietnamese allies. Me, I don't care. It's a well done movie by my standards, which merely require that I get $8.75 worth of entertainment from a movie when I pay that much for it. A low standard, admittedly, but one I can live with.
* Who in retrospect were quite obviously using the trope as a stick with which to beat the anti-Communists in both parties, right up until the USSR collapsed in 1991.