Imo Rick doesn't need Morgan to help him with his morality. Through this episode we saw Rick change his attitude. He told Michonne the truth and even gave her his gun. Michonne gives it back to him, explaining that if something happens, then it happens, but he doesn't have to make it happen. She still supports him in whatever he decides.
At the end during the meeting Rick doesn't threaten them all to take over, he wants them to decide for themselves. Gabriel leaving that gate open ended up working in Rick's favour. Something happened, but Rick didn't have to make it happen. Once Pete showed up in his state, if they weren't already on board with Rick, they certainly were after that incident.
Rick didn't kill Pete until Deanna said for him to do it. He wasn't out of control, he wasn't making them all conform to his ways. He explained his actions, he told them that they aren't ready to face what lies out there and they had to decide what to do. Deanna agreed to start doing things Rick's way by telling him to kill Pete. There's no safety in a community of you cannot trust everyone who lives there.
Pete couldn't be trusted and perhaps Nicholas and Gabriel aren't to be trusted. However I think that Nicholas and Gabriel had their breakthrough moments at the end of the episode. Glenn had every chance and reason to kill Nick, but instead he helps to bring him home. Gabriel tries his hardest to have Sasha kill him, but receives comfort and sympathy from Maggie. It's Maggie and Glenn that reach out to these 2 people, rather than give up on them. Maggie never revealed Gabriel's conversation with Deanna to anyone and I think this was because she knew how much trouble this would have caused.
Pete on the other hand was given a chance by Carol and instead of leaving it be, he resorted to violence and once he killed Deanna's husband, there was no saving him from that point.
As for Nicholas, I think he just tried to lure Glenn into the woods to kill him. He purposely climbed over the fence in view of Glenn so that he would see him and follow him. He couldn't just kill him within the community grounds, but killing him outside, no one would have known what happened. Most likely would have been torn to shreds by walkers before he died. We actually see how bad Nick is when taking on a walker. He wasn't even confident enough to stab one in the head, he resorted to using the gun, which enabled Glenn to know where he was. If Nick is going to stay alive, he'll need a lot of help to improve his fighting skills.
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