It's not an argument against absurdism, it's a different account (the correct account in my opinion) of what absurdism actually is. Life is not absurd because we die someday or because the chains of justification we'd use to explain our actions could go on infinitely as Camus proposes. Absurdity is the conflict between our ability to realize, objectively, our actions are meaningless and our compulsion to take our every day concerns seriously. Camus wants to treat absurdity as some kind of tragedy to be overcome/embraced while Nagel realizes that approaching absurdity with all the melodramatics proposed by Camus is itself absurd. Absurdity IS the human condition, it is not to be overcome, but embraced with irony. In other words, Camus sees a problem where Nagel sees none. The fact that I live in a world where I am really concerned with my career, family, and every day toils and yet consciously aware that, objectively, none of that is going to matter when the world ultimately comes to an end is the price of humanity. This acknowledgment does not require a call to change my life, to heroically rebel, or to fight with all my might the chains of socialization.
Read completely allegorically Camus' writings on the absurd can be used to support Nagel's observation, but his arguments are flawed. The framing of the emotional conflict; the awareness of the internal struggle belongs to Camus. That is why I find the Myth of Sisyphus to be a fantastic work of literature even if it fails to stand to analytic scrutiny.
No, he's arguing that Camus did not understand what the absurd really was and, therefore, failed to give an accurate account.
I'm not being narrow minded. It's my opinion and it was formed after honest exploration. Most existential writers and philosophers base their arguments on flimsy premises. Sartre, for example, would have us accept that existence precedes essence. This is a metaphysical claim that he never attempts to back up through metaphysical arguments. And yet he uses it to support his fundamental existential argument as if it were a given. He also fails to answer common objections to existentialism adequately, namely that if his brand of existentialism makes no distinction between ethical and unethical behavior.