Profoundly selfish
Donald Trump's voters are profoundly selfish.
They know that they are nominating a man who is completely unacceptable on principled grounds to a wide swath of Republican voters, yet they are voting for Trump to stick their finger in the eye of the "establishment."
They are willingly sending those voters to a third party candidate or maybe even Hillary Clinton if Trump is the Republican Party's nominee for President. They are making it more likely that Hillary Clinton will be the next President of these United States.
Just remember: You asked for this.