Your Vote Doesn't Matter
As discussed in another post, your vote doesn't really matter. Not in any real mathematical sense, anyway.
Your vote is one among hundreds of millions. And will probably be wasted, even if you don't vote third party.
So, why vote? Why take the time to do something that probably won't actually affect who becomes our next president?
One could say, "because someone died for that right," that's why you vote. Or because it's your moral responsibility when living in a democracy.
But why would someone die for a right to do something that doesn't matter? That fact doesn't somehow make your vote valuable.
And why should it be a moral responsibility, again, if it doesn't actually have an effect?
The reason you vote is not because it is powerful pragmatically, but because it is powerful in a different, and more meaningful way. It's not powerful in its effectiveness, but as a statement.
Your vote is telling the country who you want to be its leader. You're saying "I believe in this person."
Now, let's say Trump wins this election. Well, the votes for Hillary were just as wasted as the votes for Johnson. And vice versa, if Hillary wins, the votes for Trump were just as wasted as the votes for Stein or McMullin. They had zero affect on who won the election.
But, those votes serve as a statement, saying "my candidate didn't win, but I believed in them."
Pragmatism in voting is actually not very pragmatic. Chances are, your vote is wasted. Which means the mathematical value is lost, only leaving the value it holds as a statement.
Conclusion: vote your conscience.