On Page 162 of The Plague, Rambert says that he would rather die for love than for an idea. Rieux tells him, "Man isn't an idea, Rambert", to which Rambert replies that he is. In this scene, I think Rambert is really trying to justify his actions to the other two men. He is trying to show them that maybe he is greedy, but it is better than trying to play the hero.
The way I see it, Rambert knows that Rieux and Tarrou are dying for people they don't love, that they hardly even know. And he doesn't see the point in it, other than trying to be a hero, which he doesn't believe in and actually seems to view as a sort of easy way out. He is not trying to say that he's better than them for wanting to be with the woman he loves, but he definitely doesn't, or is trying to convince himself that he doesn't, see himself as somehow less than the other men because he values people he loves more than the "idea" of people.
I don't think he is trying to argue that man is inherently nothing but an idea, but I think he's trying to argue that he can become one. Tarrou and Rieux are dying for an idea. They like the idea of helping people and saving lives. Rambert also says that man is a "precious small [idea], once he turns his back on love". It kind of goes back to an idea that is central to Camus, that life may have meaning once you give it meaning. For Rambert, that is love. If there is no love, then there is no real substance, just an idea, and a weak one at that. I would have to say that I disagree, but I can see where he is coming from.
