On legalisation, as has been shown in the UK and Switzerland, tightly controlled legalisation is not going to spread addiction. In fact, many psychologists take the opposite stance. In negating the cache, the rebelliousness and anti-society stance of psychoactive usage, you are actually keeping many young people who would have otherwise experimented with them from picking up in the first place.
Having psychoactives in the niche now occupied by selected OST substances solves a great many of the world's problems: chronic illnesses like Hep and HIV/AIDs, scarcity of prison space and the whole prison inductrial complex, crime committed to support illicit addictions, the cycle of relative poverty being reinforced (by addicts not able to fund anything above their illict habit), and so on.
Legality of psychoactives and morality surrounding their usage fluctuates. Prior to 1916, the world taking the cue from the US (what else is new?), treated all psychoactives as completely legal and a matter of personal choice.
By 1923 morality began leading legislation as opposed to the converse until the mid 60s, again via America, shifted attitudes to below the 1916 baseline.
Crack in the early 80s shifted them back again until HIV/AIDs pushed them back towards controlled but legal.
So...It is a given that they will once again be legal in some way, shape, or form. The questions though are when and how?