You do not know 1% of all that can be known
This argument is a variation on the argument from ignorance. It typically goes as follows:
- Let's be very generous and say that it's possible to know 1% of everything that can be known. An atheist who says that there is no god is therefore passing judgment with only 1% of the available information, ignoring the possibility that knowledge of God might lie in the other 99%.
Lack of evidence
The fact that we do not possess all (or even most) information does not change the fact that in the 1% that we do possess, there is no evidence for any gods. It is possible that there is a god somewhere out there, just as it is possible that there are fairies or unicorns somewhere. The time to believe a proposition is when there is evidence for it, not before.
Sharing of information
Many people consider the question of whether any gods exist to be very important. If there were good evidence for the existence of a god, this would quickly be propagated through the population via newspapers, television, and so forth. Thus, if the 1% of all knowledge possessed by any given person does not include the knowledge of evidence for a god, it is reasonable to conclude that no one on Earth has such evidence.
Should we expect to have knowledge of God?
What sort of god could be hiding in the 99% of knowledge that we do not possess? If it were a lightning bolt-throwing man living at the summit of Mt. Olympus, we would be able to see his abode in satellite images. If it were some being that responded to intercessory prayer, we would see this in experimental results. If God created the universe in its present state 10,000 years ago, we would not see any stars farther away than 10,000 light years.
Since these sorts of gods contradict information which we do possess, it is reasonable to conclude that such gods do not exist. A god who hides in the knowledge that we do not possess would have to be one who does not interact with the universe in any way detectable on Earth with present-day equipment. Such a god might be impotent, or hiding (such as a deist god). Either way, there is no evidence for such a god.