A plongeur is a slave, and a wasted slave, doing stupid and largely unnecessary work. He is kept at work, ultimately, because of a vague feeling that he would be dangerous if he had leisure. And educated people, who should be on his side, acquiesce in the process, because they know nothing about him and consequently are afraid of him.
Man is the only creature that consumes without producing. He does not give milk, he does not lay eggs, he is too weak to pull the plough, he cannot run fast enough to catch rabbits. Yet he is lord of all the animals. He sets them to work, he gives back to them the bare minimum that will prevent them from starving, and the rest he keeps for himself.