Let me ask you a question: Do you think that the two-party system is good for the United States?
I find it very difficult to engage in debates about national politics because the average citizen has so little influence over these matters. I think that it's much more worthwhile to get informed about and involved in local politics, because that's where someone like me can actually have influence.
Nevertheless my own answer to the question is that it's probably not a good thing. There's this high-dimensional landscape of issues that people care and have different ideas about - reproductive rights, gun control, immigration, education, social programs, the size of government, taxation, the list goes on and on. Yet that gets projected down to this one dimensional line with just "Left" and "Right" with optional "far" and "center" prefixes.
And, sadly, the common consensus is that on election day you have only two possible boxes to check. A single decision. One bit. 0 or 1.
The Democrats and Republicans are playing a small concessions type of game. They sort of shuffle around slightly to appeal to enough of those voters who aren't already automatically voting for them. If you only vote for one or the other, they have no reason to change - they already have your vote.
Voters in safe rarely contested states, have the unique opportunity to vote their conscience without fear ((Electoral College: bug or feature?)). When I twittered about Obama's support for the FISA Compromise, Philip, a disappointed California voter replied: "our voting system forces us to vote strategically and i'll be voting obama ." This doesn't make any sense to me! Obama will carry California. Democrats almost automatically get California ((The only way the Democrats might not get California is if Arnold runs as VP for a moderate Republican, and that just is not happening this year.)) .
So why give in? You're not happy with the Democratic candidate ((There are more reasons to not be happy)), the candidate who will carry California regardless of how you vote, yet you still feel unable to voice your disapproval in the electoral arena. David wrote: "I'm not going to throw away my vote on the green party," but aren't you just throwing away your vote to the democrats, instead?
The role of third parties is to emphasize new and different ideas, to bring folks who've given up hope back to the table, and to make the major parties shift in MEANINGFUL ways. Here are some great YouTube clips on the role of third parties in the US: Part One, Part Two, Part Three, Part Four, Part Five.
If you still have doubts about voting for a third party candidate and/or you live in a swing state - consider the votepact.org proposal: find a fellow kindred heart on the other side of the political spectrum who's also unhappy with the candidate on their side, and together vote for a third party (fill out your absentees together over coffee).