Consider the Obvious!
What do we all agree about? We agree that there is existence; that something exists. An eastern pantheist claims there is no such thing as the self, and an Idealist claims there is no material universe. So we cannot get much farther than saying that something exists, and that’s not much.
So how can people inhabiting different intellectual universes discuss and debate these things? Let me suggest that we must try as hard as we can to find common ground. But that’s easier said than done. We should resist the temptation to insulate our beliefs from critique by stressing that outsiders cannot critique our beliefs. That’s a first step. Once we insulate our beliefs from an external critique we have cut off the possibility of dialogue and debate in the mutual attempt to come to the truth of it all. In fact, the more we stress that our beliefs cannot be critiqued from the outside, then the more we insulate our beliefs from a critique at all. A healthy measure of skepticism is, after all, a virtue in any other scientific or historical or criminal investigation. That’s why I have argued on behalf of the Outsider Test for Faith here at DC and in my book. An insider to a faith system doesn’t evaluate his own faith with the same kind of skepticism he uses to evaluate other faiths, so he uses a double standard. Why not approach his own faith with the same standard of skepticism he uses to evaluate the others? I claim he should. Even if not, at a very minimum he should not continually be arguing that an external critique of his faith cannot be made. He should consider these arguments anyway.
Is it possible to construct a worldview that is internally consistent but false? I think this is obviously true. Keep in mind that since no human being is a logic machine, what one sees as internally consistent may not actually be so. There are always additional premises which, when taken together with other things he believes, makes a system of belief consistent to the adherent. Here I have in mind Calvinist attempts to exonerate his God from the evil of human deeds and desires, even though the bottom line is that his God sovereignly decrees all of the evil human deeds and desires.
Let's say you are an Idealist disciple of George Berkeley and you don't believe there is a material universe. Kicking a rock and claiming to refute you won't work, will it?
Berkeley probably cannot be refuted any other way. In fact, a professor friend of mine claims Berkeley cannot be refuted. Why? Because he argued for a consistent and coherent system of beliefs.
This same professor friend argues that relativism cannot be refuted, too.
Pantheism probably cannot be refuted, either. To do so one must assume something exterior to what a pantheist believes, so it cannot be refuted from his perspective.
If we grant presuppositionalism to the Christian, then Christianity probably cannot be refuted either. But that's granting him everything!
There are other internally consistent systems of belief too. Barthianism (Neo-Orthodoxy) probably cannot be refuted.
But, these systems of belief cannot all be right. So even though these beliefs probably cannot be refuted, they cannot all be true, though they may all be false.
Unless a claim is made that can ground a belief outside the system, such a view has insulated itself from any all any critiques from the outside.
And herein lies the rub. Knowing that internally irrefutable positions cannot all be correct, the adherent of any of these religious belief systems must consider the obvious, like kicking a stone when it comes to Idealism, and the presence of intense evil when it comes to a good, omnipotent, all-knowing God.
So once again, if God is perfectly good, all knowing, and all powerful, then the issue of why there is so much suffering in the world requires an explanation. The reason is that a perfectly good god would be opposed to it, an all-powerful god would be capable of eliminating it, and an all-knowing God would know what to do about it.
So, the extent of intense suffering in the world means for the theist that: either God is not powerful enough to eliminate it, or God does not care enough to eliminate it, or God is just not smart enough to know what to do about it. The stubborn fact of evil in the world means that something is wrong with God’s ability, or his goodness, or his knowledge.
An adherent to a belief system that cannot be critiqued externally, has an intellectual obligation to consider these external "obvious" arguments. While internal consistency is definitely a test for truth, if it does not "touch ground" somewhere, it may be a castle built in the sky in a delusional world. The only way to evaluate such a delusion is to consider an external critique, and it takes a healthy measure of skepticism to do so. It means stepping outside his system of beliefs for a few minutes to consider them. Many theists won't even attempt this for fear of God's displeasure and/or his wrath.
There are Calvinistic Christians on the web who continually tell me that what I offer is not an internal critique of their beliefs, then they proceed to show me what one looks like, without reference to their own particular belief system. I know what one looks like when it comes to logic itself. But unless these same Christians can show me what an internal critique looks like WHEN APPLIED TO THEIR OWN FAITH, then they still have not acknowledged one is possible. If they want to maintain that only an internal critique of their faith can be made, then it behooves them to offer one up. They cannot continue to argue I must offer an internal critique and not acknowledge one is even possible. That's doing a dance. That's logical gerrymandering. That's peforming magic. At that point their whole belief system is unfalsifiable.