"Because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened. Professing to be wise, they became fools," Romans 1:21-22.
As a presuppositionalists, I do not like to argue with unbelievers about the evidence for and against God's existence. After all, the Bible starts with God saying, "In the Beginning, God created the heaven's and the earth." It did not start with God saying, "Here is the proof that I exist and created everything. Here is the cosmological argument, here is the teleological argument and then here is the moral theory and on and on and on ad nauseum." No, the Bible takes God's existence and His creative power for granted and only a work of God on someones heart can change them from an unbeliever to a believer. Only the gospel, working in concert with the Holy Spirit can turn a heart of stone to a heart of flesh. That being said, Roman's 1 is one of the key foundations for this understanding of theology and apologetics. We are told by Paul in this passage that God has made His existence and power manifest and obvious but people naturally hate God and, in fact, their minds degenerate to a point that their hearts are darkened and they become fools, all the while reveling in human wisdom. Here are some examples of darkened hearts and foolish thoughts/ideas.
1) All Truth is relative. This is self refuting from the start. They start off with a truth claim which boomerang backs upon them with ferocity and force. Truth cannot be relative, it is intolerant of relativism. Truth may be harsh, liberating, consoling, difficult and many other things but it does not stand amongst competing, untrue ideas and converse with them sympathetically. Truth is a tyrant, albeit a necessary and benevolent One when you truly understand Him. Even more, how do you take someone seriously who does not believe in truth? What can they say other than gibberish? How do we evaluate their comments? Can they be trusted? No, they can't. If someone does not believe in truth the best we can do in conversation with them is discuss the weather and tiddly winks. Their is no reason to take anything else seriously.
2) Fossils take millions of years to form. Google the Mt. St. Helen's volcano eruption and fossils and see what comes up. Not only did fossils form in just a few years but mountains were built! Not only do fossils form in an incredibly short period of time but it is virtually impossible for them to form over hundreds of years let along millions. Think about this. What has happened to all the dead animals that you have seen left in the elements? Scavengers come and pick to the bone whatever the maggots have left for them to eat. The fur and bones weaken, and within a fairly short period of time, within a few years, the skeleton has largely disintegrated unless acted upon by a catastrophic event: like a flood of water!
3) You cannot legislate morality. Once again, this is self refuting. It is on par with saying, "You cannot legislate legislation." Legislation is the encoding of a cultures morality and ethics. So, not only can you legislate morality, it is ALL you can legislate. Someones ethics/morality is being codified in every law, it is just a matter of whose morality is being enacted. This has really become apparent to me concerning the sexual abuse case involving Penn State and Jerry Sandusky. People who regularly comment about how we cannot legislate morality are up in arms about child sexual abuse. It is a peculiar Judeo/Christian belief that adult/child sex is wrong. The laws of our land that forbid this activity are there because of our Biblical heritage. Islam and pagan cultures have a far different understanding of this evil practice.
Here are just three examples of a darkened mind that the truth of the gospel needs to penetrate. While we can and should point out these absurdities, we must not engage in endless arguments, trying to outsmart our atheist foes. Instead, we need to share the appropriate scriptures with them, share the gospel and pray for their hearts to melt. Remember, the gospel is the power of salvation, not our intelligence, arguments or any human wisdom. God bless you friends and remember to learn, live and love the gospel!