In theory, it's very good to point to Romans 1 32 and tell people to use it as an evangelistic tool-and, granted, the subconscious knowledge of God by every person on earth may be a way of witnessing to certain people. However, the flaw in using Romans 1 32 for broad evangelism is most people aren't aware of their subconscious. Additionally, everyone else's subconscious reasons for sins are quite apparent to the person committing the same sin, but they never commit said sin for the same reason as everybody else. "I realize most people who drink all the time do it to avoid their problems, but I just like having a good time." "I know other people who burn the midnight oil at the office are doing it to get away from family problems or whatever, but I'm just really committed to this company and to getting ahead in life."
Rather, the key to witnessing to the unbelievers (and believers) around us is, in most cases, to get to know them, as Matthew 10 says. It seems in Western culture today the main point we as Christians need to get across is "True Christianity is not what you think it is."
Many today grew up being dragged to a church by their parents that was more often than not made up of hypocrites. In addition, they were told of a Father God who is distant and who can only be approached through ritual and liturgy. Or perhaps they were told God The Father is a tyrant who delights to judge and damn everybody.
Often, Jesus The Son was made to appear as a big wuss who volunteered to have God The Father beat up on Him so that the Father's rages might be satisfied.
The above paratgraphs are to say nothing of the fact that the Holy Spirit was likely deemphasized.
Of course, if the above were not enough to turn most people away from having a true relationship with the Lord, many times in these churches basic questions were never answered. Either children were told directly, "Good children don't ask questions", or the atmosphere was such that children dared not venture any queries about God.
If answers were given to anything, they were most likely unsatisfactory. Creationism, prophecy, history, and the more thorough study of human nature were likely rarely, if ever touched on.
Thus, we Christians must make it clear to people, and I myself say it now, the true nature of many of these things.
God the Father is gracious, merciful, patient, kind, and loving. These are usually traits associated with Jesus only, but God The Father is this way as well. In fact, the Father, Son and Holy Spirit are all one. (John 17 11) Thus, Father God sent part of Himself to die for our sins.
While wrath and judgment are part of the nature of God, these traits operate in the context of God's perfect love. Our whole concept of love has been so distorted in modern society that we equate love today with letting someone do whatever they want and embracing every single thing they do. God has a reason for all the laws He has given mankind and just penalties for those who disobey.
To help us in our obedience, God sent His spirit to live inside His followers. The Holy Spirit enables us to grow in God's grace, knowledge and obedience.
Not only the above is true of the Holy Spirit, but He also guides the child of God into all truth. Proverbs 25 says, "It is the glory of God to conceal a thing but the glory of kings to search out a matter." God calls His people to be a thinking people, a people who love to learn and search for the knowledge He will have revealed to them. There are answers to the big questions many theologians and preachers say have no clear answers. Prophecy can be illuminated to God's people. Knowledge of all other aspects of human existence can be revealed and shown to us by the Holy Spirit and the leading of God as well. (Acts 2 36-38)
Unbelievers need to have it clearly shown and told to them that true Christianity is not the guy with the I LOVE JESUS bumper sticker who cut them off the other day. It isn't the hypocrites who say they love Jesus in church then go out and break His law. True Christians can be hard to find, but they can be found if fellowship is desired. (Although, of course, unbelievers also need to be told that God doesn't make someone perfect the moment they get saved and that the Christian life is a growth process throughout the rest of one's earthly life.)