An easy object of scorn, and often deservedly so, in American politics is the two-party system.  Derisively referred to as "Republicrats" by some (usually denigrating the perceived corporatist control of both parties) and out-of-touch by others, the Democratic and Republican Parties are the object of scorn for many, particularly when members of one party or the other feel a sense of betrayal by one of their own or when a particular "special interest" seems to be exerting control not considered commensurate with its respective size.

The two parties are easy targets for many reasons.  Both have shown in recent years a propensity for profligate unchecked spending; for ignoring future entitlement program trainwrecks; for excessive cozying up to lobbyists and corporate interests; for using the government to force a particular agenda rather than protect liberties; for favoring expansion of the federal government at the expense of federalism (i.e., state and local control); for protectionist trade policies; and for ignoring real problems (e.g., bridges, levees, and other infrastructure) in favor of pet projects "back home".  Both parties have engaged in extreme rhetoric in attempt to paint the other as not only wrong on particular issues, but as actually sinister in essence.  Both parties have treated elections as lawyer-friendly endeavors to be fought in court rather than the ballot box.

The result of these grievous sins has been public opinion polls with unprecedented negatives for both parties and an electorate that voices its collective frustration by staying away from the polls, leaving elections to those "true believers", further polarizing the public sphere.

So does the two-party system provide any benefit?  American history and comparative analysis of other democratic systems would suggest that it provides an almost unmatched sense of stability and tranquility when matched up against multi-party Parliamentary systems of government.  The reason for this is that the Republican and Democratic Parties are each broad-based coalitions, wherein the coalitions are formed before the election.  In a multi-party parliamentary system of governance, the parties themselves might be more ideologically pure, but the elections never serve to bring those coalitions together; rather, after the election, with no party having a majority, the horse-trading begins.  Various parties have to work together, but no one party has a stake in the success of the other parties in the coalition.  Under stress, the coalition breaks apart, and new elections must be held if a new coalition can't be cobbled together.

Consider that in France, Germany, and Italy, any leftist coalition typically involves the Green Party and in many cases the Communist Party (as is currently the case in Italy, for instance).  A center-left coalition in such a situation, rather than marginalizing the Communists, actually empowers them.  They become a key cog in the wheel of the coalition.

In the United States and the United Kingdom, however, there are basically two main parties vying for the government (the UK's Liberal Democrats have risen in stature during the past couple of elections, but analysis I've read suggests this is more for purposes of opposing the war in Iraq than a true identification with the LD party; most British subjects still consider themselves either Conservative or Labour).  In the US, any candidate for, say, Congress or the Presidency must go through a primary process that can be grueling, followed by the general election; in the UK, the party insiders wield a bigger hand in choosing candidates, but there is still competition for candidates within the party structure.  To gain the nomination of the Democratic or Republican Party requires a candidate to build coalitions with the various factions of the party.

For example:  the Republican candidate in 2008 will have to succeed in a series of primaries held across the country, from more liberal states in the Northeast and California to the more conservative South.  He will have to appeal to moderates, libertarians, and conservatives; to pro-business groups and "America First"ers.  Most candidates are ideologically going to fall somewhere within one or more of these groups, but needs to at least be able to generate enough support from the other factions to keep them from sitting out the general elections.  He needs to form his coalition in advance of the election, or he will lose.  On the Democratic side, the groups are different but the concept is the same.

Because the coalition-forming occurs in advance of the election, once the election is passed the winner can concentrate on governing, rather than haggling over the terms of a governing coalition.  A full one-third of the Senate and the full House of Representatives is going to be up for election within 2 years, so a particular leader has an incentive to hold together the coalition. 

Obviously, this doesn't always happen, and rarely is political enmity greater than when a group feels as if the terms of its participation in the coalition have been egregiously compromised by a supposed ally.  Witness the recent debate over immigration as Exhibit A of this concept; the issue of immigration threatens to rip apart the Republican coalition, but primary battles, a party platform, and party convention will most likely serve to bring the coalition back together to some extent.  If that extent is insufficient, the Democrats will most likely win the presidency in 2008, and Republicans will be required to revisit the terms and members of the coalition.

The two party system is at times exasperating, but it serves a purpose:  stability of governance.  Voters in America may rue the quality of ballot choices, but post-election governance is typically not hamstrung by the failure of coalition forming.  Coalitions can change, and particular factions can gain or lose power over time without toppling the government.  Over time, this has been and should continue to be good for America.