Are voters clustered in the center of the political spectrum like a bell curve or are voters clustered in two camps at the extremes? If it's the latter, I could see the "don't vote" strategy working. Otherwise, it's bound to backfire because the leftmost candidate would need to move so far left to gain your vote that they would cede more voters to the candidate to their immediate right than they gained by moving left and lose the election as a result. They therefore don't consider you in their choice of policies and move farther right as a result, which seems counterintuitive, but it's true. This of course assumes a single political axis which isn't necessarily accurate.