1) voting third party for a national and/or statewide office when you know that you cannot bring yourself to vote for either of the major party candidates does a lot of good to building a viable third party. in most states, getting a specific percentage of the total vote in such an election means guaranteed ballot access the next election cycle. if you are actually disgusted with the offerings from the Ds and Rs, voting third party in these big elections means a viable third party has a better chance at becoming a major party at some point in the future

2) there are plenty of places at the local and state level where third party candidates can and have won election. if it is wrong to ever vote for third parties, who is putting them into office? two towns over from me is a city with a green party mayor. two towns over the other direction is another. in madison, wisconsin, at the city level the republicans are the third party -- or they were as of 2007 and i have not been active with the politics in the region since then. maine used to have a green party member of the state legislature. a green candidate almost became mayor of san francisco, only losing by 3 points in the election. these things take time but throwing your hands up in the air and proclaiming "third parties are never viable" goes against the kinds of gains third parties are actually making at the lower levels of government. if you actually care enough to vote, you should pay attention to these races because these are the people who will be running for, and winning, at the state and federal level in 10-20 years.