I find the 2 party system divisive too however what's really come to my realization due to my own study of understanding "the whys" behind the news headlines; the reactions to the OJ Simpson verdict, 9/11 and more troubling its celebration in Islamic countries, the election of Barrack Obama to the White House and the utter outrage it triggered even before he won, etc. etc. etc., is human beings seem to have an innate tendency toward tribalism. People tend to identify with and see themselves as members of groups or tribes. These groups can be political, ethnic, cultural, religious, sports team supporters, whatever. Then once they've identified with their group, the definitions or right and wrong take on type of mob mentality. Objectivity goes out the window and good, right or even better, entitled and superior become defined on the basis on membership (in good standing) with the group as well as being marked as a foe by being perceived as a member of an opposition group.
The short version is people will gravitate to tribalism. The 2 party system is in many ways a joke such as The Republican Heritage Foundation coming up with the idea of an individual mandate for healthcare coverage but a Democrat implements a Republican idea and he's a socialist. There are all kinds of other examples. I am of the view that the 2 party system pacifies the need for tribalism in the human psyche politically in America. If the parties were done away with I fear a vacuum would be created and would be filled with a political tribalism based upon geographic region and would threaten to literally break apart the country.