Why do you think "let no man put asunder" is "line-drawing"?  Granted, it can be seen as line drawing.  But not if the Gospel is taken as a whole.  The people of his day -- in particular the Pharisees -- were all about drawing lines and  satisfying the requirements of the law.  Why follow in their footsteps?  Jesus was not about giving the keys to the kingdom to those who followed the law, and then lording it over sinners.  Luke 11:46.  Jesus was about something radically different.   Turning people in a different direction -- beyond the habits of the law -- was very difficult, and remains so.  A change of direction does not often come from logical argument imposed from the outside.  It must come from within.  Jesus used every mode of communication at his disposal to jar the law-based mind sets of his listeners.  "If your eye causes you to sin, pluck it out."  Without using these precise words he also said, "if line-drawing causes you to hinder metanoia by a sinner, pluck it out."