What raises this question is my experience with hawkish atheists, who criticize religious justification for war on the one hand, yet express shock and even distain for my religiously motivated pacifism on the other. What do they expect? As a religious person I look for religious justification and divine sanction for everything that I do. That includes war. If I find war legitimate it will be for religious reasons, if I find it illegitimate it will be for religious reasons. What, do they expect me to find it legitimate for atheist reasons? I can’t – I am not an atheist – get over it.
Now of course we need to distinguish between wars which are fought on explicitly religious grounds (e.g. crusades, jihads) and those which are fought on more implicitly religious grounds (e.g. regular wars justified with recourse to just war doctrine) but either way, religious people will be looking for divine sanction before they support the taking of life. If they do not feel that sanction is there, the only alternative is personal compromise or conscientious objection.
This becomes a very sharp issue when it comes to dialogue with atheists on church-state separation. For a Christian it is very hard to justify war without blurring the distinction between church and state. It is no accident that the most hawkish Christians in America are often the very same ones with the most powerful eschatological expectations regarding the state of Israel and the manifest destiny of the United States. It is also no accident that in Australia and Britain, when just war doctrine comes up in public discourse, that it is the churches with the most solid state ties that are the very same ones that most vocally stand behind the doctrine. Quite simply conflation of church and state is extremely important for enlisting Christian support of state wars. Just ask Constantine.
Once that confusion between church and state is removed however, one of the main linchpins for Christian participation in state wars is removed with it. For separation of church and state divides our loyalties, it reminds us that loyalty to the state is of secondary concern. Thereafter we can only offer qualified support at best. Again, it is no accident that during the Reformation that Christian pacifism emerged strongest amongst the Anabaptists, those who most vocally affirmed separation of church and state. I find this consequence of state-church separation can come as a shock to atheists, who can see perfectly rational reasons for participation in war that have nothing to do with religion and want to keep religion out of it. Well we can’t keep religion out of it, we’re religious get it.