Christians had an actual dark age. Saying that North Korea established a religious free utopia is libelous and insulting, that is a totalitarian dictatorship, under the throngs of a personality cult, atheists tend to pride themselves on democracy, reason and rhetoric, this country is under fascist rule, far closer to theocracy than democracy.
If you want to see irreligious states doing well look no further than Scandinavian countries they have a mass majority of atheists, they also have some of the best education policies, eco-friendly policies and healthcare schemes in the world, with Norway recycling so successfully that it actually imports waste.
If I were to do the same to you and point you towards....I don't know, Syria or Iran and say look who a theistic utopia under god turned out everyone. Would you think that was fair.
Need I remind you as well that The USA constitution sets itself up to be irreligious. In a separation of Church and State. I am in no way using America as an example of a decent and successful nation.