This question is unfortunately very common, as in the case of Pascal's wager , most believers put this question with an attitude of defiance ("there to answer it! bet you can not!"), being visible in the illusion that the original question is that the atheist never thought of it, and will be unable to answer it.
Surprise: any atheist who is interested in discussing such issues has thought this matter, and immediately found several problems in it.
The first problem is this: it is an argument from ignorance, already mentioned here and here . This argument in this context boils down to this: "I do not know / not understand / I do not see how, once it was God." Since this is a bad argument when used in relation to something that is not yet understood or explained by science (eg the origin of the universe), since it makes sense that a supernatural explanation just win "by default", but shows more "foolish" when used in relation to something that has already been explained and understood by many people, but the believer in question does not know or understand - or tried to know or understand - these explanations. It's like someone thinking today (as it was in pre-history) that a storm is a discussion between "the gods".
In other words, is a tremendous ignorance - and intellectual laziness - to attribute emotions or one's capacity for good (or evil) "God" when they can be explained by evolution, psychology, neurology and philosophy. But learning about all this is hard work, right?
A second problem is the dualistic mentality and anti-human , it says - and is thus guilty of so much suffering throughout history - all that is profound, remarkable, important, or "good" must have a supernatural origin, outside us, a plan is not reached by the intelligence and the humanities. As the charge of Keats to Newton for having "unlocked the Rainbow" and thus destroyed the beauty and poetry of the same (as if there was only beauty and poetry in total ignorance ...), this is an anti-human mentality and anti -life, that takes the best from ourselves and say that this can only come from a supernatural plane and incomprehensible (whether "God" is anything "new age" undefined), because if it were understood and explained in purely human terms would lose all its value.
This, sorry to say, is absurd. The love of one person by another does not need an external source or justification or supernatural to have value, to make poetry and purity. Rather, the claim that these sources are needed, there is that you are taking value. What I feel for someone - a girlfriend, a relative, friend - you need no external justification, need not come from a "spiritual plane", it loses value to come "only" to me - quite the contrary, lose all and any value unless it come to me if it was not mine.
In fact, give all that is good in man to something "extra-human" only demonstrates one thing: a total hatred of mankind and himself. Something very common in many popular religions, "coincidentally".
(Note: please restrict any comment that you make to the previous question and answer, and not to other matters as the existence or nonexistence of God. Thank you.)

