They are an incredibly efficient way, however, in the USA, to:
Have slave labour drive down wages for huge swaths of the economy.
Create a disenfranchised class by fine-tuning what constitutes a felony in many states. (In 10 states a felony conviction means never voting again without a pardon. Other states have descending levels of disenfranchisement.)
Put fear in the hearts of entire segments of the population as you apply your laws unevenly.
Remember the purpose of the system is not what they say it’s for, but rather what it actually does.
Prisons are an inefficient way to rehabilitate murderers
They are an incredibly efficient way, however, in the USA, to:
Remember the purpose of the system is not what they say it’s for, but rather what it actually does.