This. Carl is a child folks. What is he maybe 13? Besides all of the normal human hormonal changes that come with his age, he is dealing with death everywhere, most importantly, his own mother whom he had to put down. Now, he has a dad going loony bin and a baby sister that will never know life before the disease.
For Carl, as pointed out, the walkers are not a real threat. He is still too naive to fully understand the dangers. This mission served three-fold...
1. Carl got a photo of his mom and (maybe?)dad for his little sister to be able to know where she came from.
2. Carl learned up close and personal that walkers will get on you in a hurry and require planning and patience to defeat.
3. Michonne gained Carl's trust.
It was important for the show, imo, to build upon Carl and Michonne's characters. It achieved that.
I give the episode an 8.