A voter in a swing state doesn't have the same luxury to vote third party and avoid a distasteful "lesser of two evils" vote.
The swing state voter not only has to directly confront the "lesser of two evils" choice, but also, more fundamentally, decide what is right and moral when one of those evils is worse than other. The easy response is to decline to vote for "evil", whether lesser or greater. But if one is convinced, as I am, that one of these evils is significantly worse than the other, is it irresponsible to decline to vote to affirmatively defeat that evil? Clearly, a vote for Clinton is a more effective means of stopping Trumpism than a vote for Gary Johnson.