When he and Rick discover Lil' Asskicker is missing, they mourn. That's more courageous than hiding pain and feelings like Bieber seems prone to doing.
Minutes after delivering his baby sister, and faced with two options: Mom as a zombie or putting a bullet in her head, Carl chose the latter. WWBD (What would Bieber do)? Faint.
After the apocalypse, Carl can deliver a baby with the added pressure of being surrounded by zombies and certain death of his mom. Bieber would cut and run.
