I'm a bit uncertain by what you call the "hard left". I don't know how one can read the "The Rebel" and come out with the idea that the author is a hardliner, when he's advocating for temperance and common sense even in the pursuit of freedom. It's true that Camus and Sartre shared some seminal ideas about religion, absurdism, and the freedom that burdens humanity. Those ideas may have formed the basis of their initial friendship, but as their respective philosophical views developed a rift also formed, with Camus rejecting the more radical notions that Sartre embraced. Again "The Rebel", which Sartre deeply disapproved of, is one such example.