I was recently engaged in debate online with a hysterical Democratic party supporter who was enraged that anyone could vote for the Greens because according to him they helped enable Donald Trump to win, and were therefore not only misguided, but evil. Jill Stein and Ajamu Baraka were essentially the devil. We have heard this one before, especially about the 2000 election when Ralph Nader supposedly allowed George Bush to win. Nevermind the unconstitutional Supreme Court judicial coup that stopped the vote count in Florida (showing that Gore won), or the 90,000 (mostly Democratic) voters stripped from the voter rolls by Secretary of State Kathryn Harris, or other vote suppression. No, it was all Nader's fault that Bush won by 500 votes.
I don't claim to have read Immanual Kant, but I was taught about deontology and the categorical imperative in a graduate school course. What does this obscure 18th century philosophical theory have to with political debates today? Quite a bit it seems.
The Democrat Perspective
There are basically two points of view. We are told that progressives or liberals have to do the practical, strategic thing and vote for Democrats to prevent the evil Republicans from getting elected. Democrats might be hopelessly corrupted, warmonging, Wall Street sycophants like Hillary Clinton, but they are the lesser evil, because they are better on social issues like women's rights, LGBTQ rights, health care, etc. Therefore, the practical thing was to hold your nose and vote for a Hillary over a narcissistic, racist, Republican con-man like Trump. I agree with Assange on this one: Choosing between Trump and Hillary was like the choice between gonorrhea and syphilis. As for Democrats in other races, we are told the same thing: vote for the lesser evil. In particular we should vote for the new batch of young progressive Democrats in order to enable Bernie's "revolution" and reform the Democratic Party from within.
The "Third Party" Perspective
The other point of view is to vote your conscience and support the person or party that most represents your beliefs, regardless of whether that action is "practical" or "strategic". This would characterize voters for the Greens, Libertarians, or other parties with a different ideological philosophy. People vote for them because they agree with their program, not because they think they will win, or otherwise change the political outcome.
The lesser-of-two-evils strategy seems to fall into the category of utilitarianism, or what Kant called the "hypothetical imperative". Wikipedia states, "These sort of actions are capable of producing good, but they are primarily motivated by a desire to meet specific purposes." This seems to define voters who demand that we vote for Democrats in order to prevent Republicans from getting elected. We must vote for Democrats because the outcome is a better one than if we vote for Greens, because Greens might "split the vote" or "syphon" votes away from Democrats and assist the Republicans to get elected. The consequences of electing Republicans (like Trump) are so horrific, especially the Supreme Court nominees they will appoint (like Kavanaugh), that we just HAVE to support Democrats no matter what. Consider what will happen to Roe vs. Wade we are constantly reminded ad nauseum. "How can you not see it? It is so blatantly obvious! What are you an idiot?"
People who vote for Greens and Libertarians are unphased by this appeal. By contrast, we "vote our conscience", because we consider it to be right, not because we expect the outcome to be good. This approach seems consistent with what Kant called the "categorical imperative". In addition, Kant asked us to consider the consequence if this position was adopted universally. Here is where the "third party" voter has the strongest case on practical grounds, aside from moral precepts. 60% of people generally don't vote for a variety of reasons, but perhaps mainly because they feel it would make no difference; Tweedledum or Tweedledee, who cares? Ironically, "third party" voters don't think their vote makes any difference either, but they do it anyway. Now if the universality principle of "voting your conscience" was achieved, and especially if everyone voted, then the outcome might be quite different.
The "Green New Deal" is now the big talking point among progressive Democrats recently elected to Congress. The Green Party was talking about this idea for years before any Democrats picked it up. The best ideas always seem to come from outside the two party duopoly. So who is being impractical now?