Scott was trying to figure out how to bridge the gap between Rick not wanting to kill Negan and Rick also really wanting to kill Negan, which he does right now [in the show’s story].
In the comics, Scott was trying to figure out why there was a hole between Rick slitting Negan’s throat at the end of the All Out War arc and then there’s the time jump and Negan is alive and in prison and Rick didn’t kill Negan.
Scott’s way to get around that was to make Carl this really humanitarian figure and person who could see the good in people and see that people can change and not everyone out there is bad.
That’s what Carl’s talk to Rick was in this episode: there’s no way that they can kill every one of the Saviors and not everyone is a bad person and there has to be some way forward than just killing people.