Here's a link to a reasonable article in Forbes which hits a point we will discuss next week in class (my 2305's are about to discuss elections and parties in the the US).
Why waste your vote for Romney and Obama if there is a candidate from a smaller party that better fits your specific preferences? Why throw your vote away?
What the author fails to note is that not voting for the "lesser of two evils" can swing elections more fully against one's interests. Votes for Nader in 2000 helped elect George W. Bush. More on this in class. It will help clarify how electoral rules in the US have guaranteed us a two party system.