It's been true throughout the world. Nobody knows what the effect would be. Anyone who tells you they know is just stupid or lying., because nobody knows. These are things that have to be tried, you have to experiment to see what the effects are. Most soft drugs are already legal, mainly alcohol and tobacco.
Tobacco is by far the biggest killer among all the psychoactives.
Alcohol deaths are a little hard to estimate, because an awful lot of violent deaths are associated with alcohol. As far as the rest of the drugs are concerned, marijuana is not known to be very harmful. It would be crazy to criminalize coffee, even though it's harmful. The United States is one of very few countries where this is considered a moral issue. In most countries it's considered a medical issue.