Answers

It's as true in Bible witness and Christian witness as in any other area that argument is fruitless.  In sales, they say that if you win the argument you will lose the sale.  In Bible witness, you can easily turn people away from Christ rather than winning souls to Christ. 

That is not to say that no one can come to Christ or come to a better understanding of Christ.  It also is true that it is important that we Christians continue to testify of Jesus.

As the wheat and tares are growing together, it seems that the tares are becoming quite mature and poisonous.  In the Church, I believe that we need to pray that we are also brought to maturity in Christ.  It seems that a life that is without contradiction in righteousness is what the Atheist and Agnostic must see.  I'm convinced that they are not seeing this very often, and the lives of Christians only confirm their godless opinion that there is no God, no Jesus, and no salvation.