There seems to be a misconception about what libertarianism is and isn't. Libertarianism is only a political philosophy. For example, it doesn't inform us about what religion, if any, is correct. Ian, and to a lesser extent Mark, seem to muddy this issue. Ian is definitely anti-Christian (not the AntiChrist) and that's fine. I, myself, am not a Christian although I wouldn't characterize myself as anti-Christian. I just wish that when he talks about religion that he would make the point that these are his personal, cultural views and not political views. A new listener may think he is one of those 'liberal" types who wants to use the state against religion.
Religion is "something one believes in and follows devotedly; a point or matter of ethics or conscience". From the meaning of religion, in its broadest definition, it is very clear that Libertarianism is a religion. Theology is only one kind of religion. The pervasiveness of theology has caused many to use it, wrongly, as the default definition of the word.
You are right to say that faith in one religion doesn't necessarily conflict with faith in another religion, but that's not to say that they couldn't. People often suffer from unresolved inner conflicts of belief.
There are different versions of both Libertarianism and Christianity and some of them are more compatible with each other than others. From my perspective though, theology requires a dogmatic way of thinking and Libertarianism, while it admittedly does have all too many dogmatic adherents to its various versions, requires rationality and the falsifiability of all of its propositions in order to be truly in the spirit of its purported objectivity.
In general, I believe that dogmatic political religions like Socialism and Monarchy are more compatible with the various Christianities and other theologies.