I believe there is a great deal of truth expressed by all the responses I read so far.
About the existence of God, for those who believe he exists no proof is necessary. For those who don't believe in God's existence no proof is possible.
This because proofs are only required by our minds and our minds cannot reach God. For those who can feel their souls, they can feel the truth about God. This is because only our souls know God. As such the soul needs no proof.
I am sure many atheist in their minds are sincere about what they believe about God. There are also many who say they know God, but they really don't. These include religious institutions. They got God all wrong.
These religions falsely claim that God is jealous, angry, vengeful and will condemn us to eternal damnation if he does not approve of us. This is far from the truth. If religions are right it can turn many away from God. Some atheists who feel the truth about who God also recognizes they cannot accept the religious views about God.
I would respect the opinions of atheist. Everyone will learn the truth about God eventually. Some will do this after death. Once in the presence of God, full of Love and Joy, everyone even atheists will see the Grand truth about God and believe in him.
Unlike the religious myth that there is only one way to God, there is actually infinite paths to God. God has a wonderful plan for all including atheists. When the dust settles everyone will rejoice. With all due respects it is futile to look for proof of God or worry that some one will prove God does not exist. Just go "out of your mind" and look into your soul.