I have tremendous respect for David Platt. I pray nearly every day for God to continue to use him mightily. I recommend listening to his sermons. You can find many of them on YouTube. David has shocked people by preaching against telling people to pray a sinner's prayer. He rightly notes that we have been guilty of communicating to people that they can be right with God by praying those words as a sort of ritual without becoming a disciple of Jesus Christ.
I agree with David. But I also believe a person cannot become a disciple without a direct connection with the Lord. That is prayer. We respond to God's embrace in prayer. If we look at the words we use as a conversion prayer, we see this intent.
We encourage people to pray a prayer of the conviction of sin.
“Lord I know I am a sinner.”
We also include repentance.
“I want to turn from my sins to you.”
If we are going to lead people to invite Christ into their life, we should warn them that they are doing business with Almighty God. They need to be fearful of praying such words without meaning them.
And inherent is the gospel is the fact that we cannot even repent without God's help. People do not come to God by their sincerity. We must come receiving His forgiveness.
“I know You died for me. I accept your forgiveness, and Your gift of eternal life. I trust myself to You.”
One of the problems with using the “sinner's prayer” for evangelism is that it is so easy. It is tempting for us because we don't have to enter into a life-long relationship with the person praying. Just get them to pray these words.
It is also too easy for the person coming to Christ. Someone can pray those words without even thinking. I also believe a person can come to Christ and truly be born again without saying the right words. We might suggest that a person think about the decision she is making over night before she prays such a prayer. Of course, we will need to be sensitive to the person and to the Holy Spirit in the situation. But You can trust Him to bring to completion the work He has begun in a person who has heard the gospel.