I think we're about to get the old Carol back.
I think what drove Morgan to abandon the pacifism was the realization that the situation was unnatural and causing people like Richard to attempt to sacrifice themselves and getting innocent people killed. I don't think he killed Richard out of anger at Richard so much as it was anger at the whole situation. I think he was angry at the realization that his pacifism wasn't going to save anyone so he intends to kill all the saviors on his own.
I actually have sympathy for Richard. I get it. He lost everything and every attempt to fight back was blocked as he was forced to kiss the Savior's asses again and again and again. I think this is what finally got through to Morgan. These people are being driven insane by repeatedly being forced to turn the other cheek.
@Cripplecreek I think Morgan had also developed a bond with Ben and was really overcome when he realized how stupid his death was---gone for no reason, over a cantaloupe. When Morgan asked Richard if he had talked to Ezekiel, and he brushed it off with, "Nah, later", the expression on Morgan's face wasn't a pleased one.
I'm not without sympathy for Richard and what he went through, and Ezekiel did need a fire lit under him. But damn, that plan was reckless.