This would be one of many heart-rending threads in this series, and in some ways still the purest and best. And Morgan comes back tonight in episode 3.12 - as Rick and Carl go back to their home town, on a mission with Michonne to get rifles and guns - and we see the terrible, bitter fruit of his "weakness," as Morgan puts it. He was only able to finally kill his walking dead wife, his beloved Jenny, when she was already killing their son Duane, also unable to fire his gun at his mother. A powerful, horribly instructive story, entirely appropriate for this powerful series.
The larger issue tonight is who can our brave human group trust? At the beginning, Rick refuses to pick up a human pleading for help on the road. At the end, going back over that same road, Rick picks something up, a backpack with whatever that the guy on the read had been carrying, and puts it in the car. It's not clear what that is. Maybe it symbolizes the pleading man, who is now beyond the need to be picked up or saved. Maybe it's Rick belatedly showing his regret for not picking the man up.
But Rick's trusting of Michonne, who saves Carl's life - Carl, who risks it to get a picture of his family before the walkers came, Carl, who did have that hideous but necessary strength (to paraphrase C. S. Lewis) to kill his mother before she turned - is completely clear now. And that trust from Rick, and the recognition that he was right to give Michonne a chance - is a key ingredient in Rick's recovery from the loss of Lori.
It was good to take a week off from the Governor, who will be back next week. What this fine standalone episode shows tonight is that what The Walking Dead is about and has always been about most is our humanity.
See also The Walking Dead 3.3 meets Meadowlands ... The Walking Dead 3.4: Going to the Limit ... The Walking Dead 3.9: Making Crazy Sense ... The Walking Dead 3.10: Reinforcements ... The Walking Dead 3.11: The Patch