It is an act of aggression as the state itself is institutionalized coercion so if you truly believe that coercion isn't the proper way for human beings to relate to one another, then why be a hypocrite and vote? If you truly believe people should exchange on a voluntary basis then one shouldn't support or go along with a charade that formalizes and guarantees the use of coercion.
voluntaryists probably already know that they are better off doing something more productive that day. . promoting agorism/individual freedom.. rather than begging for scraps in a booth.