"Which side are you on?" . . . evocative words indeed. They could be the entire lyrics for a protest song. And what are these words saying? Which group are you with! Which club do you belong to! Are you a somebody! The implication being that if you do not immediately join a group then you are an indecisive person of no character.
These days it is all the rage to have an opinion; whether that opinion is justified is irrelevant . . . as long as you have an opinion!