Should the use of cannabis be legalised to end the dealing that has poisoned life in France's banlieues, and to guarantee the quality of a substance that is widely consumed but is often of very poor quality? The economist Pierre Kopp, of Paris University, has compared the cost of combating cannabis abuse with its possible cost if legalised. He considers that, as with tobacco use, the key factor in cannabis legalisation would be the duty levied by the state: ideally that duty should be high enough to prevent increased consumption of the substance, while bringing in sufficient revenue to fund prevention.