Again I find myself comparing what Paul said to what Jesus said.

Matthew 9:10-13(NKJV)

Now it happened, as Jesus sat at the table in the house, that behold, many tax collectors and sinners came and sat down with Him and His disciples. 

And when the Pharisees saw it, they said to His disciples, “Why does your Teacher eat with tax collectors and sinners?”

When Jesus heard that, He said to them, “Those who are well have no need of a physician, but those who are sick. 

But go and learn what this means: ‘I desire mercy and not sacrifice.’  For I did not come to call the righteous, but sinners, to repentance.”

Compare that to what Paul says.

2 Corinthians 6:14-17(NKJV)

Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? 

And what accord has Christ with Belial? Or what part has a believer with an unbeliever? 

And what agreement has the temple of God with idols? For you are the temple of the living God. As God has said:      “I will dwell in them     And walk among them.     I will be their God,     And they shall be My people.” 

Therefore      “Come out from among them     And be separate, says the Lord.     Do not touch what is unclean,     And I will receive you.” 

Is Paul telling us to shun those who don't believe?  It sure could be interpreted that way.  I think there is a distinction here that Paul fails to make.

In the case of Jesus I think he is demonstrating that you have to go to where the unsaved are in order to have a chance of saving them.

In the case of Paul I think he is referring more to who you spend your time with when you aren't trying to save people.  I think he is saying don't hang out with unbelievers in your everyday life because what do you have in common with them.

Notice that Paul refers to the unsaved as the unclean.  Isn't that judgmental?  :)