The same drugs---opiates---were legal in the USA until the early 20th century, and the addiction rate never exceeded 0.3%.
Since drug addiction rates are quite a bit higher than that now ---how would making drugs legal convince the addicts to clean up? I don't see the correlation ---I think back when opiates were legal before, there wasn't welfare or Medicaid ---people probably were more motivated not to live in a drug-induced haze because they had to earn their own living.
The willing market would be huge and with our VALUEs, such as family, community, and honesty much different now than prior to WWII is also kidding themselves. The sales of opiates which would be the next easy drug for a large market would be off the charts. the 2% number would be 15% easy.