A: (Some members of the Watchtower Society may deny that the scenario posited in this question is real, but for this response I will take the question as it stands.) That is a bad application of the passage -- one of many bad applications which the Watchtower Society promotes. As Matthew 18:15 says, the instructions in v. 16 are part of a response to sins committed against oneself; this does not diminish Christians responsibility to oppose criminal activity such as child-molestation and to avoid complicity with criminals.
Also, this saying of Jesus seems directed at emancipated adults. Earlier in the chapter -- in 18:6 -- there's a firm warning against causing children to stumble; that is, the warning is against contributing to situations which would turn away children from God and tarnish the standing of the body of Christ in their eyes. Something for JW's, and everyone, to consider.
Yours in Christ,
Waterrock
