It's hard to know what to say in response. I agree with Von Dohlen. Luther's doctrine of the two realms has too often been misunderstood by both its proponents and its opponents. To bifurcate in this way is to introduce an unnecessary dualistic element. This is what occasions Luther's thinking on two realms.
Christians have a two-fold existence.
Both the secular and the sacred make legitimate claims on the Christian's earthly existence. The point of the two realms doctrine is to firstly acknowledge the duality of our earthly existence and secondly the ambiguity of earthly phenomena and knowledge. Lutherans like Granger Westberg have been instrumental in the establishment and management of institutions like the Parkridge Center for Health, Faith and Ethics because they take seriously their dual identity or citizenship. Our identity is not as either Christian or academic, but as Christian and scholar. To assume otherwise and to understand Luther differently is to bifurcate something which was intended to combat a bifurcated dualism.