Scott Sumner recently asked ("How Do Conservatives Feel About This?" The Money Illusion, 11 Nov. 2019) how conservatives feel about the fact that an increasing proportion of the population in North Africa and the Middle East consider themselves "not religious." He wonders if conservatives would like this because it means fewer Muslims, or if they would not like this because it means more atheists.
I don't think we can take "not religious" to mean the same thing everywhere. In a one-religion state, "not religious" doesn't mean atheist as much as it means "not the state religion." With no other vehicle to express religiousness, becoming disaffected from the state religion is to become not religious. However, people become disaffected for two different reasons: either they lose religion, which is what Sumner is assuming, or they have religious ideas that are in conflict with the one allowed religion. Instead of rising atheism, this could just reflect rising dissatisfaction within Islam.
I'm not going to say it's impossible that atheism is increasing in the area; it's increasing everywhere else on Earth, so it's not that hard to believe that it would be on the rise here, too. But I think the assumption that "not religious" means the same thing in Algeria that it means in Alberta is a mistake.