In Romans 1:18, Paul states that "the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth." He goes on to argue that all people have knowledge of God because God's eternal power and divine nature have been clearly perceived in the things that have been made. This knowledge of God is often referred to as "general revelation."
This passage can affect the defense of not believing in God in several ways:
It's important to note that while some like to dismiss this based the cultural and historical context in which the passage was written and the audience it was written for. However the letter to the Romans indicates that while it was written specifically to the Church in Rome, it was intended to address questions that Christians had in general and even specifically about non-believers.