The US already has one and a half million people incarcerated, which does not count all those on probation or parole. It has one of the highest incarceration rates in the world, although I think Rwanda has more, no large or industrialized country has a higher incarceration rate. Not sure increasing the incarceration rate even more is the solution.
Name another country just as free and open with fewer incarcerated. Not Switzerland for sure.
Also the incarcerated population is 1500k not 500k.
You take those 1500k and put them into some other country and have them do the same thing they did that got them incarcerated in US prison, and unless they are friends with somebody important in the government there they'll get incarcerated there too. Furthermore, in lots of countries selling / smuggling drugs is an executable offense. Furthermore, many of these 1500k would not even be admitted to enter many Euro countries with the low incarceration rates that you envy.