Impossible to make this kind of money with old-fashioned protection rackets (or gambling or prostitution) these days.

The effort for someone used to drug profits is clearly not worth the reward. Will there be a few who turn to that? Sure. But I claim that the effects on society will be miniscule if felt at all.

I would like to share your optimism, but I don't believe that sufficient evidence exists yet to back it. After all, it's not always true that changing black markets into white markets is a net good for society. There are still black markets for slaves, after all, and more slaves today than in the past, even if the proportions have gone down.