A two party system is one way to control factionalism. There are only two factions allowed, and competition between them is expected to reflect all concerns with trust - if you don't like one, elect the other.
Many Reds, Pinks and Greens seem to think that this is just a way to reflect common interests and rule common values right out of any political choice - people are voting only based on distrust and not on visions. Blues would respond that to vote based on visions is just ideology, and that it's really more important to "vote the bums out" when they get too much confidence as a ruling party - their concern is really a monopoly problem, and not the lack of any values.
This is a highly stereotyped way to discuss a complex problem in political choice and how the political spectrum views it. However, Consumerium really does not have the luxury to investigate these issues in any more detail.
See w:two party system if you really have a lot of concern on this question.