There really can be no arguing of what or who the story is about, like any work of art, it depends on the points of view of the audience. The author may have something in mind, but if he has any understanding at all, he knows full well his creation is going to be chopped meat in the minds of the million + ideologies taking their turns at it.
To me, first and foremost, it's about the futility of an aging lawman, who can't cope with the growing viciousness of crime. That's why his character is such a dud, who eventually retires over it. Moss and Chigurh are pivotal characters in creating the catalyst for his decision. The Cohen Brothers downplayed this aspect, knowing full, that suspense and action sell far better than Shakespearean inner turmoil and failure of self.
Mind you, this is simply just an example of my first paragraph: the matter of my interpretation and others will no doubt disagree or see it differently.
Isn't art amazing?