Should Christians marry non-Christians? The new testament talks of not being yoked with unbelievers - 


  2 Corinthians 6:14 "Do not be yoked together with unbelievers."


The old testament forbids intermarriage with other nations - 


  Deuteronomy 7:3 "Do not intermarry with them. Do not give your
  daughters to their sons or take their daughters for your sons."


For modern day Christians, is there any reason where marrying a non Christian is a good idea?
No, there are no reasons that would make this a good idea.

In the Old Testament we see an explicit prohibition on people inside God's chosen people marrying those outside of it on the grounds that it would cause them to turn away from serving their God.


  Deuteronomy 7:3-4 (ESV)
  3&nbsp; You shall not intermarry with them, giving your daughters to their sons or taking their daughters for your sons, 4&nbsp; for they would turn away your sons from following me, to serve other gods.  Then the anger of the Lord would be kindled against you, and he would destroy you quickly.


We see no change brought to this concept in the New Testament, however it should be noted that the outlook on "nations" is a little different now than it used to be.

Originally, it was primarily to the nation of Israel to whom God extended the offer of grace and salvation. There were some exceptional cases where outsiders were brought into that covenant, but the marriage restrictions were indicative of the fact that national lines were also belief lines. 

With the actual coming of Christ, the floodgates are opened in a new way and gentiles are grafted into the people of the promise. The national boundaries are no longer important because they do not symbolize a difference in reception of God's grace. The terminology is now to be understood in light of the spiritual family of those that have been called by God.

Marrying outside of (and becoming one with) someone outside of God's family WILL cause a rift in your fellowship with God.


  2 Corinthians 6:14 (ESV)
  14&nbsp; Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?