Are people born as atheists or agnostics? Are they still responsible for their unbelief?
Born into Sin
Before we even think to answer the question of, “Are people born atheists,” we must make it clear what Scripture says about us. To begin with, the Bible tells us that we are all born into sin. David wrote, “Behold, I was brought forth in iniquity, and in sin did my mother conceive me” (Psalm 51:5), so we must admit that the Apostle Paul is right in saying that “we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind” (Eph 2:3). Job had the godly wisdom to ask the rhetorical questions, “What is man, that he can be pure? Or he who is born of a woman, that he can be righteous” (Job 15:14)? What man could ever hope to achieve his own righteousness? None, that’s how many. The Bible tells us, “None is righteous, no, not one” (Rom 3:10). Every single one of us “have turned aside; together they have become worthless; no one does good, not even one” (Rom 3:12). Several times the Old Testament says the exact same thing: “there is no one who does good” (Psalm 14:1, 53:1). We are born into sin and are sinners in this life, so it is only because of God’s good grace that we are saved (Eph 2:8-9). Jesus is good news in Person, because Christ came to die for sinners…not for the righteous (or really, the self-righteous), but for sinners like us.
Born into Unbelief
Until a person received the Holy Spirit, they will naturally be “slanderers, haters of God, insolent, haughty, boastful, inventors of evil, disobedient to parents, foolish, faithless, heartless, ruthless” (Rom 1:31). We can’t blame them because “such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God” (1 Cor 6:11). Just like me, “you were dead in the trespasses and sins in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience” (Eph 2:1-2). We can’t point a finger and say, “Shame on them,” because “we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind” (Eph 2:3). The reason we were saved was all due to “God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved” (Eph 2:4-5). It was only because of His love, not what we did or who we are.
Since we were born into sin, we were all unbelievers, so we were atheists in that sense. We only worshipped ourselves, but when we become adults, we finally had no excuse not to believe in God, because “what can be known about God is plain to them, because God has shown it to them” (Rom 1:19). How has God shown evidence of Himself? For one thing, “The heavens declare the glory of God, and the sky above proclaims his handiwork” (Psalm 19:1). God’s handiwork is observable 24/7, and “Day to day pours out speech, and night to night reveals knowledge” (Psalm 19:2). God’s “invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse” (Rom 1:20). The truth is, “they knew God” existed (Rom 1:21a) by the creation itself, but they still denied Him anyway.
Jesus told Nicodemus that “unless one is born again he cannot see the kingdom of God” (John 3:3b). Flesh and blood will not be inheriting the kingdom, although the resurrected saints will have a physical body, but one that’s glorified. Of course, not to the extent of Jesus’ glory, but we will receive new bodies, however the bodies we have now cannot enter the kingdom. That’s good news to me as my bodies wearing out fast, and I’d hate to get stuck with it for eternity! We need a new birth for this new body! Jesus said we must repent and believe and we will be saved (Mark 1:16), so how does one become born again? It is a sovereign act of God. God grants us repentance (Acts 5:31, 11:18; 2 Tim 2:24-26), and then we put our trust in Christ, but make no mistake about it, “No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day” (John 6:44). We are born into sin and remain sinners headed down the broad path of destruction until God intervenes. God grants us repentance through His Spirit, and we see our sins for the very first time, and only then do we see our need for the Savior. The late Adrian Rogers once something like this: “If you’re born twice (physical and spiritual), you’ll die once, but if you’re born only once (physical), you’ll die twice.” You’ll die a physical death and then an eternal one, that is, unless one is born again.
Strictly speaking, we were all atheists at birth, although we did worship ourselves as we were the center of our own universe, but God ransomed us through Jesus Christ (Mark 10:45), however we can’t boast about (Eph 2:9). We are not better than unbelievers…just better off! Lazarus couldn’t boast about his contributing something so that he could be resurrected, and neither can we (1 Cor 4:7; Eph 2:1-9). We were dead in our sins, so all glory must go to God (Psalm 115:1). He alone saves (Acts 4:12), but for all those who reject Christ, they are without excuse (Rom 1:18-22). Everyone is responsible for their own sins, so why not take your sins and confess them to God. Jesus Christ died for those who would trust in Him. He says to the atheist, agnostic, and to all unbelievers, “Come to me, all who labor and are heavy laden, and I will give you rest. Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls. For my yoke is easy, and my burden is light” (Matt 11:28-29).
Here is some related reading for you: Do Atheists Really Believe There is no God? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.