Counselor: Those who believe that criticism should be gentle rather than harsh should consider the following: change requires a motive, and criticism that is unpleasant provides a motive. Since harsh criticism is unpleasant, harsh criticism provides a motive. Ttherefore, only harsh criticism will cause the person criticized to change.
The argument in the counselor's reasoning is most vulnerable to criticism on the grounds that it fails to address the possibility that in some cases the primary goal of criticism is something other than bringing about change in the person being criticized.