One thing about Carl: blaming his father for Lori's death? I guess he never realized his father chased Andrew (was that his name?) out into the courtyard, with the idea the walkers would eat him alive. That action was exactly what Carl suggested, only Andrew managed to survive. What about Tomas--or the bar guys from season 2? Rick has killed when necessary, but it is not the solve-it-all answer he's looking for.
On top of that, perhaps Lori would be alive if she never screwed Shane--which (ultimately) brought her to her demise. No pregnancy, and Lori would be alive.
When grilling Rick about missing the chance to kill the Governor during the meeting, did he stop to think the Governor was not alone? Or that an outbreak of violence could have spelled doom for Daryl & Hershel?
Further, Merle was an adult who decided to take Michonne to the Governor, just as it was his decision to release Michonne & mount his attack on the Woodbury soldiers. Rick could not alter or influence that.
Carl is a child, but his ability to rationalize is too centered on killing to prevent setting bad events in motion, when most of the deaths were initiated by bad luck, or bad personal decisions.