It seems a little historical review might be helpful.
Back in the days of Pastor Russell, Russell and his traveling representatives ("Pilgrims") would happily debate other religious leaders. Russell's message was something new and the popular religionists were not very skilled in debates.
Year passed thus; eventually a new member of Russell's flock named J.F. Rutherford had the bright idea to debate a popular religionist of the time.
Pastor Russell asked J. F. Rutherford to cancel the debate. "Judge" Rutherford was sure of his skill and ignored Russell's request.
Rutherford got his ass served to him on a silver platter by the religionist.
Since then, representatives of the WTB&TS are discouraged from participating in any debates, but there is no way of preventing the occasional prideful fool from taking the bait and re-living Rutherford's experience.