A student of Edvard Westermarck, Karsten was critical of theological explanations of religions. He was a critic of Christianity and state religion, and a proponent of freedom of religion. Karsten defended his doctoral thesis, The Origin of Worship: A Study in Primitive Religion, in 1905 at the University of Helsinki.[1] He was a member of the Prometheus Society, a student society promoting freedom of thought and freedom of religion.[2]
In total, Karsten travelled six times in Southern America and studied the indigenous people and their religions — in Bolivia and Argentine, 1911–1913, in Ecuador, 1916–1918, and in the Amazonas, 1946–1947, and others — and published extensively on them in Swedish, Finnish, German, English, and Spanish.[1] He also authored several academic course books on sociology and social anthropology.[3]