I'm not sure why Morgan is being painted like a person that outright would never kill.
His point has always been: if you can avoid it, try to. In the church, he didn't oppose to fight the Saviors.. at all. Instead, he wanted to give them a chance to surrender. In other words, a choice. Yes, the plan would not have worked, but point is, he didn't want to murder people.
Remember what he did when he faced the Wolves for the first time (and they didn't yield)? He put them in a car, and ... sounded the claxon. To attract the zombies. To an unarmed persons. He didn't kill them, but he sure didn't shy away to put them in a pinch to prevent them to pursuing him. But for all he knew, he could have caused their demise.
Whenever someone says that sometimes you have to kill, he always silently move his head, accepting it. He 'gets it'. He is not delusional. He just don't believe that killing should be the default option.
Carol is reaching there, from the opposite point. Yes, she has killed out of a necessity. But after her fuck ups, she is now understanding that you have to draw a line at some point. Finally, the fact that we saw the comparison with the Governor in the church speech, gives credence to the point that the decision was not the correct one. And they will pay for it.