A vote for Gary Johnson is vote FOR - wait for it - GARY JOHNSON. If Johnson weren't running and your choices were bad (Mittens) or worse (Obama) then you might be justified in holding your nose and choosing the lesser of two evils. The fact that every election since Nixon in '68 - and probably before that - have been framed by the Repugnicons as "the most important of our time - or ever - is beside the point completely. If Johnson reflects your views then vote for him.
Vote FOR him.
If in the future libertarians (like me) who have decided to hitch their wagons to the Stupid Party in hopes of changing it from within should manage to get a classic liberal on the ticket, then by all means vote Repugnicon. Mittens, however, ain't that guy.