Dutch leniency is aimed at isolating and controlling a problem under supervision of the authorities, but there appears to be an increasingly consensus: It has grown out of hand.

Ed van Thijn considers himself a tolerant man, but he readily admits that he is no longer as broad-minded as he was when he became mayor of Amsterdam in 1983. At that time the Dutch city of 700,000 was notorious as the drug capital of Europe, a place where hashish…