Time to really drive it home for Fantine. After selling her hair and her teeth, and working herself sick, she figures she might as well sell the "rest," a.k.a. turn to prostitution. Way to pile it on, Hugo! Sure, he might be exaggerating just a teeny bit, but the point here is to force us to see, over and over, how lack of compassion and understanding contribute to human suffering—the suffering of a specific human, not just some abstraction we can cluck our tongues and pray over.