Even if someone doesn't approach an atheist and talk to the "atheist" about God and Christ they are condemned anyway because whether they like it or not God's existence is shown to them by the things that are around them. Closing one's eyes and refusing to see doesn't make the whole situation go away.
Romans 1 Authorized (King James) Version (AKJV)
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness; 19 because that which may be known of God is manifest in them; for God hath shewed it unto them. 20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: 21 because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
I live in a very earthquake prone country. If an atheist was trapped under a pile of rubble of a collapsed building and a fire was beginning to move in their direction I'm almost certain they would be saying "Dear God please save me, please save me, please don't let me burn to death, please get me out of here".
Whenever I talk to non-believers about the things in this world that could never have come about unless God created them then the non-believers always want to end the conversation and run away. I became a Christian because of the things I saw around me and knew therefore that God who was unknown but known to me at that time must exist and I also knew I stood as guilty and condemned for wrong things I had done in my life. You can imagine my surprise when I read scripture for the very first time like that quoted above.
As Chris pointed out. You can try and tell people, but if they won't listen all one can do is let them go their own way.
Here's a sneak preview of the "atheists" in the future.
Revelation 6 Authorized (King James) Version (AKJV)
12 And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood; 13 and the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind. 14 And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places. 15 And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bondman, and every free man, hid themselves in the dens and in the rocks of the mountains; 16 and said to the mountains and rocks, Fall on us, and hide us from the face of him that sitteth on the throne, and from the wrath of the Lamb: 17 for the great day of his wrath is come; and who shall be able to stand?
It looks like their "atheism" won't last very long when rocks start falling from the sky. "Dear God please save me, please save me, please don't let me burn to death be crushed under a big rock falling out of the sky, please get me out of here".