Because it's there

What George Leigh Mallory told a New York Times reporter when asked why he wanted to climb Sagarmatha/Everest?

Well yes, but also the answer given by the chair of the Advisory Council on the Misuse of Drugs (ACMD) when asked why magic mushrooms were in the same category as heroin and crack - Class A - in the system defined by UK drug laws, according to The Guardian yesterday.

The ACMD says drugs currently classified too high up the scale shouldn't be moved down because this would encourage their use, and those classified too low down shouldn't be moved up either... because this would encourage their use.

So the answer is to keep everything exactly as it is, because it all works so well.

(The Misuse of Drugs Act 1971 categorises controlled substances by class - A, B and C - according to how dangerous they are perceived to be, and by schedule - 1 to 5 - which sets out how you can legally use them. A drug's class defines the maximum penalties for its illegal use).