Perhaps that is true in terms of maximizing your influence in the next election.
But to maximize your influence over a longer time period, you should vote for the third party candidate that most closely matches your views.
Then, when the major party candidate you would have resorted to loses, the post mortem reveals votes lost to the candidate you voted for, and in the subsequent election the major party adapts its platform to win some of those lost votes.
If politicians expected voters to vote on principle and to hold them accountable, we'd have an entirely different sort of politicians.
> But to maximize your influence over a longer time period, you should vote for the third party candidate that most closely matches your views.
That might, arguably, resemble truth if the details of the political system itself were guaranteed stable over time and not subject to alteration by the same people who gain power over other policies through electoral victories. But, in the real world, to maximize your influence over a long-time period, you should organize and advocate for both electoral reform and the minor party you most prefer during periods between elections (the former to work to mitigate the perverse effects of the existing system, the second to maximize the likelihood that, in the next election, the competitive major parties -- which can change over time -- will include the party you most prefer.)
But, once its clear who the major candidates are in the present election, you should still generally vote for the one least harmful to your interests if they win.
> If politicians expected voters to vote on principle and to hold them accountable, we'd have an entirely different sort of politicians.
With no changes to the electoral system, what we'd have with that is "major" parties representing even smaller pluralities (well, technically, only the biggest would be a plurality), and more negative campaigning directed by each major candidate at getting voters best served by the other to not vote for them to "hold them accountable" for something. Which is a change of degree, not kind, from what we have now.
> you should organize and advocate for both electoral reform and the minor party you most prefer during periods between elections
I totally agree with this.
>Once its clear who the major candidates are in the present election, you should still generally vote for the one least harmful to your interests
I don't agree with this, because the platform-creation calculus of the major parties is to ignore interest groups that will not abandon ship.
As H's platform makes clear, when there is sufficient loyalty, it's in the best interest of the candidate to edge as close as possible to the opposing party's platform, to attract as many swing voters as possible.
But to maximize your influence over a longer time period, you should vote for the third party candidate that most closely matches your views.
Then, when the major party candidate you would have resorted to loses, the post mortem reveals votes lost to the candidate you voted for, and in the subsequent election the major party adapts its platform to win some of those lost votes.
If politicians expected voters to vote on principle and to hold them accountable, we'd have an entirely different sort of politicians.