Apart from the fact that (1) this view begs the question (cf. Micah 4), it must also be asked (2) why redactors felt encouraged to add these passages to Isaiah if the original form of the prophecy was so uniformly negative. Why not to Amos or Micah or Jeremiah? For that theory to be accepted, the original form of the book will have had to have contained the Judgment/Hope motif in more than a germinal way.
The chief reasons for this are theological, for it is argued that the glowing predictions of salvation to come are not to be found in preexilic prophecy. Apart from the fact that (1) this view begs the question (cf. Micah 4), it must also be asked (2) why redactors felt encouraged to add these passages to Isaiah if the original form of the prophecy was so uniformly negative. Why not to Amos or Micah or Jeremiah?