I discussed with a friend the other day my "rationalism". Instead of trying to defend how I function, rather I wanted to try to explain it. When dealing with infidels, you cannot use the Bible. As an Evangelical we learned how 'historically accurate' the bible was. Indeed Homer's Illiad might be historically reliable, but this doesn't mean Apollo played a role in the fight. Rather than go this route, I tend to use Metaphysics in the Thomistic method, or go the route of the New Natural Law theorists, who put forth basic goods for human flourishing and argue how Catholic doctrine is in keeping with this. I believe in reason / common sense, because I believe humans are created in the image of God. If they were not, then obviously reason would be useless. If we are totally depraved as Protestants contend, it is likewise useless.
Much of my conversion was based on the reasonableness of Catholicism. History attests to Roman Catholic Ecclesiology, and Tradition is reasonably the most suitable interpreter in scriptural difficulties. To put it simply, Catholicism makes sense. I think a person's philosophy (epistemology) determines their theological views. Unbeknownst to me, a Political philosopher I encountered at Brock converted me from Protestant Nominalism to Aristotelian Thomism. This laid the groundwork for everything else.
I am not a Rationalist if by that word you mean one who believes in Reason alone, or seeks to eliminate religion. But rather I am someone who holds the Anselmic doctrine of faith seeking understanding. I believe in reason, which to most postmoderns makes me a Rationalist. I found a part of the Catholic Encyclopedia which explains my position best:
"The term Rationalism is perhaps not usually applied to the theological method of the Catholic Church. All forms of theological statement, however, and pre-eminently the dialectical form of Catholic theology, are rationalistic in the truest sense. Indeed, the claim of such Rationalism [Enlightenment Atheism] as is dealt with above is directly met by the counter claim of the Church: that it is at best but a mutilated and unreasonable Rationalism, not worthy of the name, while that of the Church is rationally complete, and integrated, moreover, with super-rational truth. In this sense Catholic theology presupposes the certain truths of natural reason as the preambula fidei, philosophy (the ancilla theologiæ) is employed in the defence of revealed truth (see APOLOGETICS), and the content of Divine revelation is treated and systematized in the categories of natural thought. This systematization is carried out both in dogmatic and moral theology. It is a process contemporaneous with the first attempt at a scientific statement of religious truth, comes to perfection of method in the works of such writers as St. Thomas Aquinas and St. Alphonsus, and is consistently employed and developed in the Schools."
While folks like Chesterton had to contend with Rationalism and thus fell towards the faith side of the equation, it was never Fideism which Kierkegaard and so many Protestants and postmoderns alike are fleeing to. In this day and age, the balance needs to swing back to rationality (in my opinion).