@khird I think this misses half the picture. There are two primary effects your vote may have and both need to be considered in tandem..
1) what is the chance of you casting a decisisve vote
2) what effect does it have on future voting if you increase the percentage voted for a third party..
If you vote is not decisive then the effect your vote has is limited to #2.. if you vote primary party then your vote is telling people "hey primary party will always win, third party doesn't stand a chance, don't vote third party"..
So in short when your vote is not decisive you are ultimately voting whether you want to increase the chance of a third party win and higher voter support in the future or not.
Since the chance of your vote being deciscisive is so astronomically unlikely no matter who you vote for we can rule out #1 entirely, it doesn't even matter if your vote stands a slightly higher chance of being decisive for a primary party than a third party because its still so statistically small as to be effectively impossible.
Therefore #2 is the only actual consideration in play... do you wish to perpetuate a two party system and encourage it remain two party into the future, or not.
@khird Well no, im not talking about ballot access alone, or even bragging rights.
Most people will not vote for a third party because they feel voting for a aprty with a small chance of winning is a waste of a vote. Therefore by voting third party you increase the number of people that voted for the party and thus with larger portion of support people who use the above logic as a reason not to vote third party no longer have a valid excuse and thus will be more likely to vote third party int eh future.
So while ballot support is one element worth considering the argument is entierly valid even if that factor is not considered at all.
Remember the USA has changed primary parties 9 times in its lifetime. In all cases the changes following non-linear trajectories where the third party had almost no support, there is a marginal increase in support and that increase quickly snowballs, breaking the third party mentalitya nd resulting in a third party replacing a primary party. This has been the pattern in all historic cases.
So by increasing the support of a third party you effect actual good by encouraging the transition of the third party to a primary party due to the perception of the general public, which can have results in only a single election year based on historical observations.
@freemo I don't think I missed that - it's what I meant by "marginal utility" of a vote in the last full paragraph. But it's highly dependent on your jurisdiction - if your state doesn't have a mechanism where you qualify for easier ballot access in future, or some other direct benefit, then it's basically just bragging rights: "I got six hundred seventy-*three* votes, not six hundred seventy-*two*!" And what's that worth to the candidate - moreover, what's that worth to you as the guy voting for him?
If enough minor-party candidates get enough votes, maybe it eventually contributes to the decline of the two-party system - but that takes hundreds of thousands of votes across many races, so you're back to the problem of your one vote having negligible impact, just like the guy who voted for a major-party candidate.
Alternatively, instead of taking two hours off to stand in line and vote, go home with two more hours' worth of wages in your pocket. Which is the better expected value?