As is appropriate, let us start with Kant. Kant looked upon a world of tutelage in which thought was bound by outside direction. Therefore, his answer was to "dare to know," to use reason to pierce the veil and discover the true nature of reality.
Kant's problem, however, was the subjective nature of his use of reason--but not just its subjective nature, but in the subjective-use-of-reason's objective claim. Kant didn't think society as a whole could handle intellectual freedom at first. Yes, he said, if freedom is granted, enlightenment will follow, but he also thought the social order needed to be guided to enlightenment by guys like Kant. I think this is because Kant might have been afraid of pluralism, afraid that others would use reason to arrive at conclusions at odds with Kant's own. It might not have been all that, but in any case Kant's problem was a narrow view of where reason would take us, what enlightenment would look like.
Years later, there was Barth, who claimed that reason should not be our guide. Human rationality is not to be trusted. We can't know anything by merely following our intellect. Truth can only be given to us by revelation from God.
Barth, however, probably needed to learn a lesson from Hegel. The lesson is that nothing is immediate, for everything is mediated. We cannot simply be passive recipients of revelation, blank slates onto which God places the knowledge of the truth. Everything that comes to us is mediated by our context, our finite scope, our presuppositions, our previously established categories, and so on.
My point against Barth is that we cannot not use reason. Even if God reveals something to us, we have to use reason to receive that revelation. Barth himself wrote around 10,000 pages of theology, clearly showing us that we do, will, and must use reason to receive anything with our minds.
Freud's point against Barth is that not all of us can experience [what we interpret as] revelation. Not all of us can have religious experience. You say you had some kind of spiritual awakening, some kind of religious experience of God? That's wonderful for you, but what can I do with that?
Reason, on the other hand, Freud says, is something we can all use. Not all of us can use "revelatory" religious experience as a guide, but all of us can use reason.
And, I say again, all of us do use reason. Van Til used his reason to say that we all have presuppositions, ones we cannot avoid. He rightly pointed out that there is no neutral plain on which we can make judgments about the universe. There is no untainted lens through which we can look in order to decide what is more or less true. Thus, he so reasoned, the best thing to do is presuppose the Bible as the Word of God and the key to universal truth....
Van Til needed to read Freud, though. Freud would say, why the Bible? And why in that way? It's not that simple for all people. It's not that simple for people of other cultures, or people who don't have Bibles, or people who engage in critical study of the Bible, since they get to consider that if the original writers of the Bible knew that their writings were incorporated into a larger work and then used as the key to universal truth, they would most likely be baffled and maybe even appalled.
Additionally, that is no reason to adopt something as true. "Well, none of us can know what is really true because our vision is tainted by presuppositions, so let's just grab whatever thing we want and hold it up as the beacon of truth. Who can prove me wrong?" I hate to refer to Richard Dawkins, but couldn't we just do the same thing for the flying spaghetti monster?
No, that just won't do. The nice thing about reason, on the other hand, is that it is something we all can use. And so, even if we agree that no one of us can adopt a neutral, presupposition-less stance toward truth, we all can (and do!) use reason to find a path to truth.
However, in order to avoid the enlightenment overreach, we need to qualify that search for truth with the postmodern critique of Kant. That is, we do not have access to objective truth. We can't know Truth, capital T, as Cornel West says; we can, he says, only talk about the way to truth.
Thus, rather than saying reason is the way to Truth, I say reason is the way to the way to truth. While we will never arrive, we can make progress, and we can be led to a truth-claim. It is then important to acknowledge other truth-claims and their validity. This is the importance of pluralism. Because no one of us has that perfect vision, we have to pay attention to what others are seeing, and learn from them, and engage them, and respect the diversity, humbly acknowledging our intellectual position as finite.
The problem of enlightenment rationalism was not its emphasis on reason, but in its lack of self-awareness and epistemological humility. Reason is the way to the way to truth, but so is humility and an embrace of pluralism. We are not the center of the universe, as Kant would lead us to believe. It is not MY reason that leads to truth, it is reason's engagement with the reasoning of others.