Jeff,
Taking CovenantInBlood's comparison of Romans 1:18 to related Scriptures (always the proper approach in cases like this) a step further, the following Scriptures come to mind:
Now the serpent was more crafty than any other beast of the field that the LORD God had made. He said to the woman, "Did God actually say, 'You shall not eat of any tree in the garden'?"
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But the serpent said to the woman, "You will not surely die."
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Then the LORD God said to the woman, "What is this that you have done?" The woman said, "The serpent deceived me, and I ate." (Genesis 3:1,4,13 ESV)
Why do you not understand what I say? It is because you cannot bear to hear my word. You are of your father the devil, and your will is to do your father's desires. He was a murderer from the beginning, and has nothing to do with the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies. But because I tell the truth, you do not believe me. Which one of you convicts me of sin? If I tell the truth, why do you not believe me? Whoever is of God hears the words of God. The reason why you do not hear them is that you are not of God. (John 8:44-47 ESV)
The coming of the lawless one is by the activity of Satan with all power and false signs and wonders, and with all wicked deception for those who are perishing, because they refused to love the truth and so be saved. Therefore God sends them a strong delusion, so that they may believe what is false, in order that all may be condemned who did not believe the truth but had pleasure in unrighteousness.
But we ought always to give thanks to God for you, brothers beloved by the Lord, because God chose you as the firstfruits to be saved, through sanctification by the Spirit and belief in the truth. (2 Thessalonians 2:9-13, ESV)
These and passages too numerous to quote buttress the fact that
all outside of Christ deny, as did Adam, the truth of the Word of God through unbelief. That is why Paul's phrase stands at the head of his argument running from 1:18 to 3:20 that "there is none righteous"; rather than describing the subset of the exceptionally wicked, whose deeds he goes on to detail in 1:19-32, it describes all in Adam, all of whom are described throughout the following verses.
Suggestion, if your friend raises objections, challenge him along these lines:
1) if the people of 1:18 "who suppress the truth in unrighteousness" are a mere subset of humanity and not all, are the deeds described in 1:19-32 representative expressions of the unrighteousness of this group of people?
2) if so, have you ever committed any of the approximately 40 specific categories of sin* listed in those verses?
3) if so, you have acknowledged yourself to be a suppressor of the truth in unrighteousness.
4) if not, reading 2:1-3 will require you to acknowledge that the very fact that you distinguish between those guilty of God's wrath--based on their deeds which you judge--and yourself, is proof sufficient to acknowledge that you have yourself suppressed, in unrighteousness, the truth about your own lack of righteousness before God.
Let us know what develops. Will pray that his eyes be opened--to the truth.
* 40 categories of sin
refusal to honor God
refusal to give thanks to God
futile thinking
darkened hearts
claiming wisdom
becoming fools
exchanging the glory of God for images
impure lusts
dishonoring of bodies
exchanging the truth about God for a lie
worshipping the creature rather than the Creator
serving the creature rather than the Creator
dishonorable passions
homosexual acts
refusal to acknowledge God
debased mind
doing what ought not to be done
unrighteousness
evil
covetousness
malice
envy
murder
strife
deceit
maliciousness
gossip
slander
hatred of God
insolence
haughtiness
boasting
invention of evil
disobedience to parents
foolishness
faithlessness
heartlessness
ruthlessness
doing what is known to deserve death
giving approval to those who do what deserves death
