Also, they were convicted in trials, for violating laws that were written by an elected legislature, and signed into law by an elected president. They were also provided an attorney, and have an appeals process at their disposal.
Seriously, yes, our prison system is really, really screwed up, but we got here largely out of public myopia and apathy, and to indicate we arrived at this place for reasons bearing any similarity to North Korea's is ignorant, at best.