This is the sorcerers' guild. It was founded to undertake requests to kill monsters, known as reaper's quests.
The guild dispatches its sorcerers far and wide to slay monsters that were once human. Essentially, it is an officially-recognised body that deals in murder.
All those who work for the guild obey what is known as the Sorcerer's Code : all monsters must be slain.
It is believed that those who give in to greed and desire are bound to repeat their mistakes. The severity of the punishment is to match the sin of the beast.
For these reasons, it is not permitted for sorcerers to save monsters. But it should not be forgotten that sorcerers are humans too. Tormented by their duty, on occasion they offer salvation to the beasts they have been sent to kill. The guild tends to turn a blind eye to this.
But should a sorcerer persistently violate the Code, the guild is known to hire ... contractors. In such cases, they say that the sorcerer in violation will pay with his life.
The sorcerers that are part of Avalon tend to sacrifice more. This is due to the fact that the will hand out rewards for those without mercy.
In short, the more you sacrifice, the more rewards you get.
Not only that, but while bounded to Avalon, sacrificing Archfiends, Foul Creatures and even other players will give you more Sacrificing Experience.