Carol literally fought him when she found out he had a Wolf prisoner. Both she and Rick have told him that not killing is not an option. In the last episode, when Morgan was rattling on about how that prisoner saved Carl, Rick's WTF face told me he's wondering how to handle Morgan now. I don't think that was "Gosh, he may be right about this circle of karma," so much as "Is it safe for this dumbass to be near my family?"
As for the jail cell, the fight over that is coming when (if) he tries to actually use it. Do you think Rick "I don't take chances any more" will permit that?
I'll come back to this: Morgan is wrong. We know it. He knows it. He stated that explicitly. It's just the writers exploring how people cope with an irretrievably hostile world.