The reason I'd consider voting for Sanders is that he might be able to more effectively address my policy concerns--dealing with climate change, reducing poverty, increasing social mobility, increasing economic growth (what the gov't can do there is stabilize the financial system and address downturns with rational fiscal policy), and preventing major foreign wars. If he were to lose, voting for Ted Cruz or Rubio would go against all of that, as would declining to vote. The "voting for the person whose image you like better" thing is completely alien to my way of thinking.