This is already happening: Throughout Britannia there are thieves, assassins, and various other illicit professionals who kill and destroy for no reason other than personal glory and happiness. Most are never truly happy, despite the lengths they go to in order to "get what they want." Often it may be a blood lust or a sense of honor lost that drives senseless fighters and thugs into battle. At times death is the outcome of a mistaken phrase.
So why should spellcasters have anything to do with these thugs? They shouldn't, but for the riches that are offered by those who seek powerful spells without the discipline of training to earn them, some spellcasters would do anything. The Council has been established in order to establish a justice system for dealing with magi who cross the lines, as well as any who breaks our code of honor:
The restricted spells that are included are here. The "cases of life and death" are reviewed by the council promptly. If it is decided that the spells were in abuse of the code, swift action is taken wich may result in loss of spellcasting privileges. Those who uphold the code are never gone unnoticed. The council welcomes new candidates to apply to join at any time.
You may be a member of the guild and not the council, but not vice versa. All members of the guild are expected to obey the code, regardless of anything! It is for the glory of honor we do this, and if it saves our lives, the lives of loved ones, and saves the glorious land of Britannia, the loss of honorless weapons and spells is of a small matter.