Honestly and without sarcasm: from what I understand, it seems like pretty much everybody in North Korea is a prisoner of North Korea. Not having control of your own life, being constantly monitored, and not being allowed to leave are all hallmarks of prison life. Add to that starvation and retributive acts against your family by the state itself.
Let's not get caught up in hyperbole here. North Korea is a harsh dictatorship, but even then, you get to live, breathe the outside air, have a family, raise kids, and you don't risk being raped at every turn (as in physically raped, let's not mince words here and go on a tangent about "mental rape by the state" or whatnot).
It's probably choosing between two kinds of hell, but if given the chance, I'll 100% no-questions-asked go to live in North Korea rather than be incarcerated 10 years in a US prison. (It goes without saying that I'd rather live free in the US, I hope this doesn't need saying. Also it goes without saying that I'd rather live in another country rather than North Korea; this is a thought experiment where these are the only two options).
Of course, prison in North Korea must be hell too, but that's not what we're talking about.
Finally, comparing the US to North Korea -- is that really the bar we want to use?