Magic mushrooms are no illegal to posses even if not processed. Picking them is illegal.
The thing with drugs is ever since the dawn of conciousness in humans they have used drugs of one sort or another and different cultures use different drugs.
Different drugs have different levels of ill effects – both on individuals and society – from "E" which is very safe to alcohol and heroin that cause so many problems.
No one take "E" and goes out fighting on a Saturday night, nor do they go robbing folk to pay for their next "E"
Tomahawk – the slippery slope hypothesis is generally accepted as discredited these days – take Holland – cannabis is easily available so people who want to get high take that. There are far fewer heroin addicts in Holland than here – perhaps because the easy availability of cannabis means folk don't need to try other drugs as they can get high any time they want.