Known risks with quantifiable outcomes
Ralph Nader and his advocates still claim they did not influence the 2000 election results, Bush winning. Bush then killed 4500 US troops and countless other people unsuccessfully working out his oedipal flaws.
The US election system stinks but that's the voting landscape to be negotiated. Don't step in the dog turds. A vote for Stein, Johnson, or Harambe *is* a vote for Trump.
And as for the repeated claims that congress/senate/DOD/states would obstruct any Trump stupidity, so that it doesn't matter what idiot gets elected president, see Bush et al. Oh, and the recent wailing "I didn't think my vote would count!"