Carl’s Vision of Hope
In these visions of what might be, Carl was picturing an idyllic world where there was peace and prosperity. There was food and shelter. People were clean. (Kind of a big deal on this show) People were wearing nice clothing. All of these things seems basic until you figure that they’re only possible when there is peace.
There are three possible outcomes in All Out War with the Saviors: Negan dies, Rick dies, or Negan lives. (I suppose they could both die, but that would be pointless and way too destructive to the story)
Carl wants the violence to end. His vision includes Negan because if Negan is there then it means that the war is over and everyone is alive and well. Sure, there won’t be immediate peace, but given the time jump in these future visions, it’s quite possible that something, something could have happened to allow everyone to put the past behind them and live in harmony.
Having Negan in Carl’s visions is the ultimate sign that there will be peace some day and it will be a wonderful thing.