It is simply recognising the realities of cannabis/psilocybin use, the fact that the law is not working and that the people who get punished are often individuals who use these socially and are not hardened criminals in any sense of the word.
Cigarettes and Alchohol are licensed drugs, yet more violent crime is associated with alchohol use than with cannabis or mushrooms.
It would cut a source of income for dealers and raise revenue at a time when the deficit is at an all time high.
It would decriminalise people that use the drug, but not those that sell it illegally (although by legalising it their market would disappear overnight).
Medical evidence shows that cannabis is no more harmful that alchohol and tobacco which are licensed, therefore the rationale for making it illegal is flawed.