Couple of things. Both Morgan and Carol have flaws in their methodologies.
We know Carol's motivation, She has no one to really live for besides herself and is determined to not be a victim any more. She's loyal to Team Rick but only as means to an end (her own survival). The problem is she making calls beyond her authority. Rick recognized this when he asked her to leave the prison, but since Rick has slid closer to her mindset now, he gonna overlook it. In some ways, Rick is taking his lead from Carol. She's been subtly working him toward overtaking Alexandria since they got there.
Sooner or later she's gonna make a call on something which Team Rick is not gonna stand by her on. There's a reason they showed that whole hospital scene. The intent was to show that "Some people" are worth making the attempt to save, even if the chance is low. Whereas Carol just snuffed that Alexandria kitchen club chick who had gotten stabbed with no hesitation. She's gonna do that on the wrong person someday.
Morgan clearly knows how to defend himself, he's not soft on zombies at all, but he takes chances with other survivors that seem illogical. We don't know his motivation. We know he was completely deranged at one point and he was able to come back from that and become even more capable at the same time. We don't know how yet. His grip on the world is tied to this "new code" he adheres to. I really look forward to learning how he got to this point.
The indefensible action that Morgan took last night was an attempt to take a hostage in the middle of the battle. Strategically, it was the right move because you need to find out where these people are coming from and what their motivation is. Tactically, its dumb to try to hogtie someone safely with a battle ranging around with you. The only reason I can think the writers did that was just to show how ruthless Carol was when she shot dude who was no longer a threat.
His action wasn't indefensible he just did not killed them.
I don't remember them trying to kill him last season but if that is right.....
How can taking a hostage be the right move if he knows them?
Their intentions was clear the minute they start to attack and their motivation is to survive by any means necessary. We see the lengths they will go to achieve that.
I think I was the first to say Morgan was weak when the whole argument about tyrese came up but I will say this....
White ppl have a long history of using violence to construct masculinity/manhood. Some of you adhere to this idea of about "having a soul or empathy" when in reality they see it as a sign of weakness and incompetent to survive.