When you take the opinions of many reasonably informed people, each serving what they feel is the public good, you get a reliable and rational public opinion. Collective deliberation means that the public is exposed to debates, discussion and reflection, exposing them to other viewpoints. If the public is only exposed to one viewpoint, that viewpoint will most likely be the one they support. But if experts debate, and the debates are covered by the media, the public will have more choices and a better understanding. The majority opinion will become a collective deliberation, because it is the collaboration of multiple views.
Today there are articles, books, publicized debates and speeches available to the public.
They are exposed to more then just the most popular opinion. Even political conversations between neighbors help to refine and enlarge the publics' views. All these things add to the rationality of the public. However, a problem may arise if the minorities' opinions are not heard. A recent example of this is the limiting of the 2000 Presidential debates to the democratic and republican parties.