Despite his status, Charlie is a compassionate and extremely empathetic demon.  She is genuinely upset by the thought of harming other demons.  Although she knows that souls go to Hell for a reason, but because of their terrible deeds, Charlie still considers the Extermination pointless.  Her main personal goal is to help sinners escape this through self-improvement and perhaps redemption.  However, it seems that Charlie is the only one who believes in this.