Why do Athiests require 'proof' that God exists?

[Oldandeasilyconfused]

You can easily prove your own existence!

Not sure that's actually ever been done. Not everyone accepts Rene Descartes' "cognito ergo sum". Me? I'm agnostic on the matter,but lean towards the positive.

Of course you may have another argument ,which I would probably find incomprehensible; I barely grasp the criticisms of Descartes.

There have been a number of criticisms of the argument. One concerns the nature of the step from "I am thinking" to "I exist." The contention is that this is a syllogistic inference, for it appears to require the extra premise: "Whatever has the property of thinking, exists", a premise Descartes did not justify. In fact, he conceded that there would indeed be an extra premise needed, but denied that the cogito is a syllogism (see below).

To argue that the cogito is not a syllogism, one may call it self-evident that "Whatever has the property of thinking, exists". In plain English, it seems incoherent to actually doubt that one exists and is doubting. Strict skeptics maintain that only the property of 'thinking' is indubitably a property of the meditator (presumably, they imagine it possible that a thing thinks but does not exist). This counter-criticism is similar to the ideas of Jaakko Hintikka, who offers a non-syllogistic interpretation of Cogito Ergo Sum. He claimed that one simply cannot doubt the proposition "I exist". To be mistaken about the proposition would mean something impossible: I do not exist, but I am still wrong.

Perhaps a more relevant contention is whether the "I" to which Descartes refers is justified. In Descartes, The Project of Pure Enquiry, Bernard Williams provides a history and full evaluation of this issue. Apparently, the first scholar who raised the problem was Pierre Gassendi. He points out that recognition that one has a set of thoughts does not imply that one is a particular thinker or another. Were we to move from the observation that there is thinking occurring to the attribution of this thinking to a particular agent, we would simply assume what we set out to prove, namely, that there exists a particular person endowed with the capacity for thought . In other words, the only claim that is indubitable here is the agent-independent claim that there is cognitive activity present[5] The objection, as presented by Georg Lichtenberg, is that rather than supposing an entity that is thinking, Descartes should have said: "thinking is occurring." That is, whatever the force of the cogito, Descartes draws too much from it; the existence of a thinking thing, the reference of the "I," is more than the cogito can justify. Friedrich Nietzsche criticized the phrase in that it presupposes that there is an "I", that there is such an activity as "thinking", and that "I" know what "thinking" is. He suggested a more appropriate phrase would be "it thinks." In other words the "I" in "I think" could be similar to the "It" in "It is raining." David Hume claims that the philosophers who argue for a self that can be found using reason are confusing "similarity" with "identity". This means that the similarity of our thoughts and the continuity of them in this similarity do not mean that we can identify ourselves as a self but that our thoughts are similar.[citation needed]

http://en.wikipedia.org/wiki/Cogito_ergo_sum