No arguments from me about how terrible Lori was. She was not written that well for the show.
Lori's death resulted in complications which could probably be blamed as a failure to perform a significant sweep of the prison, but she was pretty much the worst character in the show in my opinion up until she died.
Logically, that's obvious. But Carl is a child who looked to his father as this ultimate protector, as any child would. Rick was a sheriff, he pretty much "rose from the grave" in season 1, he protected the family and kept them safe above all else
The group staying in the prison was a group decision, Rick merely put it on the table. Neither of these things were necessarily Rick's own fault, which is why Carl's sudden rant about how it was Rick's fault stirs the disgust people have with his character.