It seems to me that we would be better served to discuss the differences of Objectivism vs. Subjectivism, not Rationalism.
Objectivism (metaphysically speaking) is the belief that reality exists outside of one's perception or conciousness. Objectivism says that if a tree falls in the woods and no one is around to hear it, it still makes a crashing sound.
Subjectivism (metaphysically speaking) is the belief that reality only exists within the confines of perception. In other words, for someone that subscribes to Subjectivism, the tree makes no sound, since no one hears it.
Rationalism takes no stance on the existence of God, nor is it humanistic in nature. It relies solely on factual analysis and reasoning, rejecting faith based arguments. Empirical knowledge is a cornerstone of modern day Rationalism, thus forming a fairly strong link to Agnosticism. It is the Rationalist that rejects rhetoric in political arenas, while looking for that rare nugget of truth (if there is one in politics). :roll: