By saying that US is one of the most free countries I meant in terms of freedom of expression and relatively better opportunities to pursue different careers and lifestyles, freedom to have almost any kind of hobby, freedom to not be bound by traditional cultural norms and freedom to go to and join any kind of party. Most prisoners in US are not in there for "insulting a government official", "insulting a royal subject", "blasphemy", "membership in an undesirable organization", being an Uighur, and so on.

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.