I've voted third-party a number of times, but that's because I've lived in unflippable states and I'm playing the long game. If you care about the short-term results that are this specific election and are in a state where it can change the results, voting third-party is the wrong choice. Not voting is an even more wrong choice--"both are bad and I'd like us to have better choices in the future" can best be achieved by voting third-party. "Both are bad, so I'll let other people decide" seems less likely to influence future elections, and it's obviously not the right way to effect this election. The one economic principle I always cite rings true here: Rational people think on the margin.
People who think abortion is infanticide saw an opportunity to fill the Supreme Court with justices who might ban abortion. Given their goals, not voting would have been a worse decision than voting for Trump was.
That seems like a false dichotomy. There were third party candidates. Plus, you can always choose not to vote.