Separation of Church and State

How is a Christian who is situated in a society where church and state are separated able to form cogent beliefs about the morality of the state? For it would seem that the severance of church and state, when taken to its logical conclusion, would entail a Christian being severed from thinking about politics with reference to their religious beliefs. A Christian would then, in forming beliefs about the morality of the state, have to resort to some other moral foundation than that of their religion. Would this not inevitably result in an outright rejection of their Christian ethics?

Pacifism in Anabaptist Theology Does Not Oppose Old Testament and Government Violence

To my surprise, my last post appears to be consistent with Anabaptist theology, at least, one particular account of it. Lynn Martin over at Anabaptist Faith writes in a post: "Let me emphasize that by no means should the doctrine of nonresistance be interpreted as against secular violence or Old Testament violence." See the article "Early Church Fathers on War, Violence, and Pacifism" for more information if interested.