I've never seen my friends so divided by an election before. Some are voting for Clinton because Trump is just that bad. Others are voting for Trump because Clinton is just that bad. And probably the majority are planning to vote third party for various reasons.
I'm generally in favor of voting third party. If no one ever does, it pretty much guarantees that the two major parties will be unresponsive to their bases, because they know the base will never abandon them -- or if they do, they'll stay home, in which case it's really hard to say exactly why they didn't turn out. A third-party vote says, "I'm committed and involved, and this is the sort of candidate I would have voted for."
As long as your vote is guaranteed to a certain party, you have basically no say. The party knows you won't vote for anyone else, because you're too scared of the opposition, so they don't really have to work for your vote at all. This is, in my opinion, why the prolife movement never makes any progress. They've made it quite obvious that they will never vote Democrat, and they also are so scared of Democrats that they rarely vote third-party either. That means all a Republican candidate ever has to do is be just barely less pro-choice than the Democrats, and all the terrified prolifers fall in line. It is not necessary to have a prolife voting record or to actually pass any prolife legislation while in office. He just has to say "sanctity of life" a couple of times on the campaign trail once or twice, and that's a whole bloc that's all his. Lobbies that are more bipartisan, whose supporters will withhold a vote as needed, get a lot more done. (Apparently the gun lobby is famous for this.)
So I'm heartened that people are finally drawing a line somewhere and withholding their vote from the candidates they don't like. That's the only way you get better candidates.
On the other hand, if you always vote third party and never for a major party, you're in the same boat. Your vote can't be won, so no one will bother with you. (And by "you" I mean mainly your issues and groups, because no one is tracking you as an individual of course.) Every year there is some small percentage who vote Libertarian or Green and it's pretty obvious that no mainstream candidate will ever satisfy these people. So no one actually caters to those groups. To have an effect politically, you have to be the sort of person who has both standards and realism. You have to both understand that politics is about compromise and perfect candidates aren't available, and be willing to draw a line somewhere and deny your vote to candidates who are truly unacceptable.
That is, of course, if you're voting third party because you hope to influence the two major parties to care more about your issues. That's not the only reason people do it, though. Some people do it because they believe that you are morally complicit in everything the person you vote for does, but you aren't responsible for a person you didn't vote for, even if you could have kept them out of office with a different vote. I don't see that. You don't "keep your hands clean" simply by voting for people who you know won't win, because your vote isn't just about picking your favorite person but also about the effects you have on the result as a whole. If you don't vote for Joe, and Bob wins instead, you're not really any less to blame than if you voted for Bob. (Well, perhaps 50% less, since you would have put Bob two votes ahead if you had voted for him.) That's a consequentialist ethical view for you, but where voting is concerned I don't think it can be anything but a consequentialist question. Voting itself is morally neutral, and it seems the morality of the vote is in the foreseen results, not in how morally upstanding the guy you voted for (or didn't vote for) was.
Another reason people vote for third party candidates is because they think that if everyone did it, those candidates could win. I used to think that, too -- that deep down everyone wanted libertarian candidates and just didn't vote for them because they were scared to. But after further experience, I think that isn't true. Libertarian ideals are popular in maybe 10% of the population, and maybe another 10% would settle for a libertarian candidate because they hate the major ones so much. But the reason the major parties do well is at least partly because they have wider appeal. People like liberty, but not too much, and not for people they don't like. Likewise, socialist-type candidates are popular in a certain crowd, but most people don't really want a socialist in power. They just want some basic programs. Pacifists, sadly, are not a big lobby with any party, and as I talk to people I realize it's because people don't actually agree with pacifism.
It's easy to get confused about this because we hang out with people like us, and we know everyone we hang out with likes some of our own pet issues. But most of the country doesn't. They care about lower taxes, or more government programs, or a more interventionist military, or less immigration. These are ideas that appeal to large swaths of the country, and the two parties have divvied them up in a way that isn't really perfect for anybody but which is good enough to still get votes.
But think about it: when ten friends try to decide on a place to go for dinner, or a movie to watch, what are the odds even half of the group gets their first choice? If two want pizza and three want burgers and four want tacos and one isn't really hungry, they are all going to have to bargain and compromise until they come up with something that no one actually hates. And that's if they're lucky and get along well. It's the same in politics -- there are so many issues and so many possible positions on these issues that if each person actually dreamed up their ideal candidate, it's unlikely that any two people would be thinking of exactly the same thing.
So we all compromise. We decide that we're willing to compromise on foreign wars but not abortion, for instance, or immigration but not welfare. And that's how we find our way into one party or another, or voting for one candidate over another. The second part of this process is a bit more sketchy -- often we rationalize the compromise we've made, or pick up ideas from other people in our party, and convince ourselves that we actually do believe in foreign wars or immigration. It feels better to think we're not really compromising, and that way we feel less out of place among our political allies.
Despite the suboptimal nature of this process, though, it does work. Everyone gets some of what they want. While democracy doesn't give everyone all of what they want, it does ensure that the decisions that are made are actually wanted by somebody. Sometimes it seems way too messy and frustrating, and we all wonder if there isn't a better way. Certainly there are things that could be better about our system. Even with a perfectly set-up system, there is never any such thing as 300 million people all getting what they want. (Except in capitalism, whoooo! But not everything can be decided that way.)
So, if your analysis leads you to vote third party, you should do so. There are cases when it may do some good. I think it's important to take the long view instead of listening to fearmongering that This Is the Most Important Election in History (every election in my lifetime has been described that way) and therefore we must all crowd behind a candidate everybody hates just because nothing could ever be worse than getting the other one. Sure, there are some candidates so bad it might be best to beat them in the short term and worry about strategy later. (I think Donald Trump is one of those candidates. It kind of shocks me that some Sanders fans are willing to let him win rather than compromise -- he clearly is opposed to almost all that they stand for.) But you can't do that year after year if you expect your voice to be heard. You've got to do what you can to push the major parties more into line with what you want -- which will include things like voting in primaries, voting in local elections, donating to campaigns, and knocking on doors. It may also include not voting for "your" party's candidates, if they don't meet some basic minimum standard. I think it additionally includes voting for that candidate if they do meet a basic standard. They won't be perfect and you might not like them all that much, but if they'll really forward some of your main issues, you should reward them with your vote.
Well, that's what I think, anyway.