Because one of them *HATES* you.
Trump has indicated he hates Americans, wanting to drive our standard of living into the toilet, making our effective wages a third lower. He's declared war against our Constitution, attacking the First Amendment and demonstrating antipathy for limited government and America's foundations.
And he has shown every intention of going after these things with vigor.
Meanwhile, Trump supporters have been trying to convince me that Hillary is low-energy, and therefore not nearly as much of a threat. If I'm going to have a liberal tyrant in the Oval Office, I suppose it makes sense to want one who isn't as driven.
Still, those who prop her up may still act with vitality and determination. Therefore, I think they are both very dangerous, and I can't vote for either.