So, we have a problem. For some reason, we think that all politics fit into two cosmically-opposed, innately human categories, "liberal" and "conservative." We are very wrong. The evidence is everywhere. It's in "conservatives" trying to change abortion law, pro-life catholics allying themselves with the labor movement, Ron Paul (and other libertarians), spread across the history of politics (see Teddy Roosevelt, the hawkish trust-buster, enemy both to capitalism and small invade-able countries), and this message board. Binary thinking is useful for human beings, which is probably why we use it so damn much. We try to view things in terms of opposites. Consider taste - there are five completely distinct sensations available to the human tongue, but we often divide with "salty" and "sweet." When it comes to politics, binary thinking really hurts us. In a two-party system, you don't necessarily need your base to like you - they just have to hate the other guy more. Thus, we see both of our parties slowly converging on the middle, chasing after the only votes that aren't already in the bag, swing votes. This has an effect on the electorate itself. Individual citizens come to think that they have to be (for example) anti-gun and pacifist if they also want gay marriage and socialized medicine. Recognition of this fallacy - that there's nothing about gay marriage fundamentally tying it to gun control - leads some to practically worship centrism, as though it were a holy grail to rescue us from the nasty extremists. (You know, compromise is often only 3/5ths of a good idea.) In a system with at least three parties, there would be a world of difference. For one thing, one would be able to break party lines without automatically being a centrist. (You might agree mostly with the opinions of two parties, switching between them for individual issues, while finding the third to be mostly vile and wrong.) It would also allow us to be more open-minded about politics, and the result would be a greater diversity in American voters' opinions. People who have views that are seemingly contradictory in a binary system would finally be able to vote for a candidate they can identify with. If you google "political compass," you'll find a system for mapping political differences that I think is superior to just "left and right." I don't think it's perfect, but it comes close enough to be more useful than not.