The existence of non-belief is contradictory to the very idea that the Christian God exists.
There are lots of people in the world who do not have a belief in a God. Furthermore, according to each religion on earth, there are billions of others (outsiders) who do not believe in the correct God, and who will therefore be punished, in some way, due to their non-belief in their specific conception of God. But how can anyone acknowledge "the right God" if they are completely unaware that this deity exists and wants certain things from them?
Now according to Christianity the following are true:
-A conscious personal being called Yahweh exists and created the universe and everything in it
-Yahweh is omnipotent, omniscient, and omni-benevolent
-Yahweh wants every person to know the truth and be saved
-Yahweh provided a means for every person to be saved
-But this being has not made it apparently and unequivocally known that the above are true
According to Christianity, in order for one to be saved it is necessary for one to think the following are true:
-You have committed sins against him
-Yahweh is willing to save you from the punishments of those sins so that you can be saved
[These 3 will be called "X" herein]
But if Yahweh wants us to be saved, and wants us to know these "necessary" things, why don't we know them? I think the most reasonable position is that we (non-believers of X) don't know them because the Christian God does not exist.
P1 - If Yahweh exists he desires that we know X
P2 - If Yahweh exists he has the power for us to know X
P3 - If Yahweh exists, given 1&2, we should know X
P4 - We do not know X
C: Given 3&4 Yahweh does not exist
1. But God doesn't want to "force himself" on us. He gave us freewill which would be violated if he just showed up and made us all know X.
Response: Knowledge does not negate choice. Even Christians agree that God demonstrated himself to angels, the prophets, the apostles, etc. So just b/c one has knowledge of a thing doesn't at all negate our freewill to choose to follow or obey.
2. All non-believers in Christianity are actually "secret believers". They "suppress the truth in unrighteousness" and know X but refuse to acknowledge them.
Response: Many non-Christians and/or non-theists display ample demonstrable evidence that they are actively seeking the truth and badly want to know God (who/whatever "it" is) in as close a relationship as possible (as well as know X). Where is the evidence that people are secretly Christians, let alone theists? It seems there just isn't any good reason for thinking this claim is true.
3. We are sinners, and b/c of sin we refuse to acknowledge Yahweh as Lord and repent.
Response: This response is similar to #2. There simply is no reason for thinking that all non-believers of Christianity/"Jesus is Lord" around the world are somehow incapable of connecting with an omnipotent deity merely because they are "sinful fallen beings" (short of merely assuming what needs to be proved). Isn't Satan a sinful fallen angel? What about all the angels who supposedly saw Yahweh and still rebelled? They must know he exists. How about Judas Escariot?
In addition, it seems quite contradictory to say that God wants us to know X but that we still don't know X due to our "sin". Are we more powerful than Yahweh (an omnipotent being)? Obviously, according to believers, this being has no problem with demonstrating the whole of nature to us, in a way that we can actively seek knowledge without necessarily having certainty of it. So why not demonstrate himself to us in the same way - so that (at the very least come judgment day) we won't have an excuse.
4. It's all part of his divine plan. For those who do not believe, Yahweh will eventually reveal himself to all of us at some point (perhaps at the of the earth) and there will be none who claim not to know X.
Response: This is the typical answer when one has no good answer. It is akin to saying, "I just have faith" which doesn't get anyone anywhere b/c anyone can 'just have faith' in anything. This response is insufficient because it leads to answering an apparent contradiction by a mere personal promise which is derived in the very assumption the Christian has made in his/her bible. "Oh, sometime out there we'll know later." It doesn't bring us any closer to a resolution to the problem.
So then Yahweh does not want us to know, and act in accordance with, X right now? He would rather us continue "in our sins" and not do "his will", preferring rather that we do "the work of the evil one" here on earth? This seems quite contrary to the message that Yahweh allegedly wants all his "children" to be saved (and to be saved right now) and do his will. Do you think your God does not want non-believers to be saved right now?
5. Yahweh wishes that all would be saved but that is not possible because he only chooses a few. We don't know why but we just believe and trust the bible.
Response: But why trust the bible? What sound evidence do you have that this collection of ancient writings in divine? Can you provide anything uniquely sound that cannot also be said of other claimed holy books? In a round about way this response seems to admit that the bible contradicts itself (for example that God wishes that none should perish, 2 Peter 3, but that he has prepared some for "destruction", Romans 9). Why should we put ANY trust (let alone our entire lives) in this belief system? There seems no good reason we ought to do so.
So then once more, the existence of non-belief is contradictory to the idea that Yahweh exists, because if it did we should except to see far greater numbers of "saved" Christians (indeed ALL people) and far less "souls burning in hell". Therefore we ought to feel confident in thinking that this being called Yahweh is not real.