While I've heard that line as a reason for Christians to not marry non-Christians, I've not heard it used as a reason to have nothing else to do with people who do not believe. I do appreciate your effort to get back to the original topic of this thread, instead of atheists and believers trying to proseletyze each other.
What should Christian believers do in regards to their atheist neighbors? What is wrong with them finding common ground as Americans (in the US, of course) who ratify the idea of religious freedom?
This:
NIV Matthew 10:7-15
7. As you go, preach this message: `The kingdom of heaven is near.'
8. Heal the sick, raise the dead, cleanse those who have leprosy, drive out demons. Freely you have received, freely give.
9. Do not take along any gold or silver or copper in your belts;
10. take no bag for the journey, or extra tunic, or sandals or a staff; for the worker is worth his keep.
11. "Whatever town or village you enter, search for some worthy person there and stay at his house until you leave.
12. As you enter the home, give it your greeting.
13. If the home is deserving, let your peace rest on it; if it is not, let your peace return to you.
14. If anyone will not welcome you or listen to your words, shake the dust off your feet when you leave that home or town.
15. I tell you the truth, it will be more bearable for Sodom and Gomorrah on the day of judgment than for that town.
NIV Mark 6:7-12
7. Calling the Twelve to him, he sent them out two by two and gave them authority over evil spirits.
8. These were his instructions: "Take nothing for the journey except a staff--no bread, no bag, no money in your belts.
9. Wear sandals but not an extra tunic.
10. Whenever you enter a house, stay there until you leave that town.
11. And if any place will not welcome you or listen to you, shake the dust off your feet when you leave, as a testimony against them."
12. They went out and preached that people should repent.
NIV Luke 9:1-5
1. When Jesus had called the Twelve together, he gave them power and authority to drive out all demons and to cure diseases,
2. and he sent them out to preach the kingdom of God and to heal the sick.
3. He told them: "Take nothing for the journey--no staff, no bag, no bread, no money, no extra tunic.
4. Whatever house you enter, stay there until you leave that town.
5. If people do not welcome you, shake the dust off your feet when you leave their town, as a testimony against them."
NIV Luke 10:1-11
1. After this the Lord appointed seventy-two others and sent them two by two ahead of him to every town and place where he was about to go.
2. He told them, "The harvest is plentiful, but the workers are few. Ask the Lord of the harvest, therefore, to send out workers into his harvest field.
3. Go! I am sending you out like lambs among wolves.
4. Do not take a purse or bag or sandals; and do not greet anyone on the road.
5. "When you enter a house, first say, `Peace to this house.'
6. If a man of peace is there, your peace will rest on him; if not, it will return to you.
7. Stay in that house, eating and drinking whatever they give you, for the worker deserves his wages. Do not move around from house to house.
8. "When you enter a town and are welcomed, eat what is set before you.
9. Heal the sick who are there and tell them, `The kingdom of God is near you.'
10. But when you enter a town and are not welcomed, go into its streets and say,
11. `Even the dust of your town that sticks to our feet we wipe off against you. Yet be sure of this: The kingdom of God is near.'
NIV Acts 13:47-52
47. For this is what the Lord has commanded us: "`I have made you a light for the Gentiles, that you may bring salvation to the ends of the earth.' "
48. When the Gentiles heard this, they were glad and honored the word of the Lord; and all who were appointed for eternal life believed.
49. The word of the Lord spread through the whole region.
50. But the Jews incited the God-fearing women of high standing and the leading men of the city. They stirred up persecution against Paul and Barnabas, and expelled them from their region.
51. So they shook the dust from their feet in protest against them and went to Iconium.
52. And the disciples were filled with joy and with the Holy Spirit.
Our job is to point out what their 'freedom' will finally get them.
There does come a time when one can no longer keep a child from playing in the street.