Really? Why is that?
If you think about it countryboy, a dictatorship is pretty much like a religion. A dictatorship has certain beliefs, the dictator is supreme, he gives out rewards and punishments, it is not really much different from religion. The important difference is of course that in a religion, the Messiah or God threatens you with eternal damnation, eternal torture after you die, the dictator threatens to do it while you are alive.
But there are many similarities. Since Atheists do not bow down to any God, they would not bow down to any dictator either. The first people that a dictator wants to eliminate is independent thinkers, Atheists are the original independent thinkers.
So different dictatorships may put different factions in concentration camp. Nazis may put homosexuals, Jews, Communists there, Communists may put religious people, those who are disloyal to the Party there, Christian, Muslim Fundamentalist dictatorships will put other religions in concentration camps.
But you can be sure that they all will put Atheists in the concentration camp first. So it doesn’t matter whether the dictatorship is Nazi, Communist, Islamic Fundamentalist or Christian Fundamentalist, you can be sure that people like be will be the first ones to be herded into concentration camps.