Let me first say that I'm not actually one of those Democrats who thinks that third party challenges need to be squashed, or that the people who vote for leftist third party candidates are somehow actually supporting Republicans. My feelings on the matter are as follows:
A vote for a third party candidate is not the same as voting for a Republican. Instead, it is effectively the same as not voting at all. While no analogy is perfect (the truth is that voting for a third party candidate is the same as voting for a third party candidate), this one holds up much better to logical scrutiny. Other than the extremely rare situations where third-party candidates have a shot at winning, voting for a third party candidate ultimately impacts the outcome of the election in the same manner as not voting at all.
No one is entitled to votes. If progressives or Independents or whoever end up voting for third-party candidates, then the Democratic nominee just didn't do a good enough job winning those votes. Period. It isn't the fault of the voters--it is the fault of the candidate.
We shouldn't expect, or even desire, consensus. We would indeed live in a disturbing version of a republic if no one voted for third parties, if everyone voted, and if everyone was enthusiastic about one of the two major party nominees. Dissent via third parties, via not voting, and via "holding one's nose" is healthy for any republic. While third parties and not voting tend to be just about the least effective forms of dissent available, it would still be a shame if the 1-3% of the country that voted third party every two years went away.
Now, with all of that said, as I explain in the extended entry, I still don't want anything to do with third-parties. While they should not be existentially scorned, for anyone who actually wants to change the American political system, the ineptitude of third-parties is indeed worthy of scorn.
Third-parties in America are weak, inept, and ineffective. For example, third-parties are actually less effective in presidential elections than in congressional elections, but still idiotically run for President more than they run for Congress. In 2004, the total third party vote for President was 1.00%. In 2006, the total third party vote for the U.S. House was 3.16%. And yet, we are treated to the likes of Bob Barrs, Cynthia McKinney's and Ralph Naders's every year, while third parties rarely run for Congress at all:
Libertarians contested 73 particular U.S. House seats in both 2004 and 2006, and the competitive conditions for each of those 73 seats was the same. That is, in all 73 instances, there were the same number of major party candidates in the race both times (i.e., either both times there was both a Democrat and a Republican in the race, or else both times only one major party ran anyone).
In these 73 elections in which the conditions were roughly the same in both 2004 and 2006, Libertarian percentages increased in 42 districts and decreased in 31 districts.
The Constitution Party contested 12 such U.S. House elections in both 2004 and 2006. Constitution percentages were up in 8 of those districts, and down in 4 districts.
The Green Party contested 11 such districts in both 2004 and 2006. Green percentages were up in 4, and down in 7.
Despite only running a combined 96 candidates for the 435 seats of the U.S. House, these three parties will all run a candidate for President of the entire country this year. For a comparison, Democrats will run between 420 and 422 candidate for the U.S. House this year. Further, third party candidates actually perform much better in House elections than in Presidential elections, and yet these parties tend to focus on the Presidency than they do on the House. Quite frankly, that is childish, and demonstrative of a general lack of seriousness. If these parties don't take themselves seriously, and actually run candidates across the country and in the elections where they can make more of an impact, then why should anyone take these candidates seriously?
With rare exceptions, as forms of political engagement, third parties are extraordinarily ineffective. They don't push new messages or new ideas into mainstream discourse. They actually result in less respect and less influence within the major parties for both their ideas and their membership. If people don't like the nominees of the two major parties, there are many more effective ways to engage the system, from community groups, to media activism, to issue oriented work, to primaries.
In short, while I think existential attacks at third parties are both misplaced and misguided, I also don't hold a high opinion of third parties because I view them as the epitome of political ineptitude. If all the third-party candidates in the country this year combine for 1.51% or more of the Presidential vote, I will be shocked. The reason Cynthia McKinney isn't in Congress anymore is because isn't a very good politician, at least relative to the other members of Congress. Much the same can be said for Bob Barr. While Ralph Nader never held public office, he was excellent for a while at building infrastructure, pushing progressive issues into mainstream discourse, and even passing laws. He probably should have focused on those areas, because he doesn't seem very good at winning votes.
But, I'm not here to concern troll for Ralph Nader. As I said above, if there weren't Bob Barrs and Cynthia McKinneys and Ralph Naders, we would live ina pretty disturbing version of a republic.