Gabe is probably the most rejected person from the point of view of Rick's core group.

He just might be Morgan's first student. Gabe wants to learn. And Morgan wants to teach. They both said they are not good at guns. (So said Morgan but I remember he still carries his rifle along when he left Eastman's cabin.)

So, if Gabe wants to learn the skill to kill, he will ask Carl. If not, he will go to Morgan for lessons.

 

I can't see that happening. It's too far removed from who Carol is. Carol is merciless, but she's not running through the woods stabbing random people. Neither is she locking someone in a cell and starving them to death for 47 days. Carol doesn't really kill senselessly. Some of the people that she's killed have indeed come across very brutally and perhaps unnecessary, but it's ultimately been in the name of her own survival. The killing that Eastman and Morgan have done was not necessary. Morgan turned to the aikido because he needed to center himself and regain his sanity. Carol has never lost her sanity. She's cool and collected in basically any situation. She realizes that Morgans philosophy isn't how a person survives in the ZA.