Ok, really liking the discussion
Now I have to point out something here:
We don't care whether or not God actually does exist, only whether belief in God is justified.
You cannot separate the issue this simply. I think weather God actually exists or not makes a pretty big difference in weather believing he exists is justified.
What I mean is that if someone has a "
ersonal encounter with God" - he is either right or deceived. In the Christian view, humans actually have this "sensus divinitatis" - a sense that allows them to know God. This, for example, would work by looking at a beautiful mountain and suddenly thinking "God is majestic" - This sense of the divine (Rom. 1:18-22). Now, sin can damage this sense, to the point of completely distorting it, just like you can go completely blind.
Now, if Christianity is true, than believing that God exists based on this "sensus divinitatis" is quite justified - it is a properly functioning faculty.
If Christianity is not true, then there is of course no sensus divinitatis, and anything thought to be believed because of it is not justified.
You see how it makes a difference if God actually exists or not?
Now, I promised a further argument earlier, and here is my rebuttal to the only other alternative that seems to be viable in this discussion: Naturalism. Of course there are more views, but as far as I can tell most folks participating in this discussion are either naturalists or theists.
So is it rational to believe in naturalism? Well, if naturalism is true, then all there is is matter and energy. There is no mind, only a brain. And a brain is completely explainable in terms of brain chemistry and physics. Each time you "think" a thought, what really happens is that a certain number of neurons in your brain are caused to fire by some trigger, and as a result you have the experience of having a thought. When you reason, that is what happens. You do not really reason, certain neurons in your brain fire and send electrical signals to other neurons, who also fire.
From here I will develop two arguments that you cannot get to reason:
1. All that is happening is that chemicals and molecules, and groups of those are flying around a certain part of the universe (generally referred to as your brain) in certain patterns. But how do moving molecules have anything to do with truth. You could describe, theoretically, the position of every single atom in your brain for a certain amount of time. However, why would such a state of affairs have anything to do with reason? Furthermore, what causes these molecules to move the way they do? Well, science would have us think one of either two things:
1. Normally, nothing happens without a cause. As a result, all the molecules flying, neurons firing, everything the "brain" does is actually caused and thereby - determined. All those thoughts you think "YOU" are thinking, every time you think you are making a rational decision - you are actually just observing the universe doing its thing, and you can't do a thing about it. Therefore, you can't reason. Therefore, believing this is not rational.
2. Ok, so you may argue that ever since quantum physics we have the principle of indeterminacy - quantum events are not determined. So instead of observing the determined universe happening, you are now observing the random universe operating around you. This, actually makes it even less likely that anything like truth would lie anywhere in those events you notice going on. And you are still not free, you are "being randomed" - you can't reason, so your not rational.
Ok, now for the second line of the argument. Even if you do not quite buy the story above and say that, molecules or not, who knows why I am conscious, but I am. So how did you get to have the brain you have. Well, that is pretty clear on naturalism: Evolution. So if evolution is true, what kind of brain are you going to develop? Well, here is atheist philosopher Patricia Churchland (she said it, not me):
Boiled down to essentials, a nervous system enables the organism to succeed in the four F's: feeding, fleeing, fighting and reproducing. The principle chore of nervous systems is to get the body parts where they should be in order that the organism may survive⦠Improvements in sensorimotor control confer an evolutionary advantage: a fancier style of representing is advantageous so long as it is geared to the organism's way of life and enhances the organism's chances of survival. Truth, whatever that is, definitely takes the hindmost.
So, as a result your brain is not primarily designed to be rational or to reason, but to survive. Even if your brain might be able to be rational, you would not know, because for all you know, when you think you are being rational, your brain may be fulfilling quite the different function. As a result, you cannot rationally believe that you are rational. You are irrational
Now, of course, if theism is actually true, than you have a brain designed by God for the purpose of being rational and can actually make arguments. So the only way you can rationally argue for naturalism is if theism is true. Either way, you lose