My friend and I used to always make fun of the character of Sherman McMasters in Tombstone (starring Kurt Russel and Val Kilmer).
He is played by Michael Rooker from The Walking Dead, among other things.
So, for the first two acts, McMasters is just your regular henchman, he rides with the Cowboys, they start trouble, show up at a Spanish wedding and murder everybody there, basically a group of thieves and murderers. If he had any moral compass, he would have quit riding with The Cowboys a long time ago.
So, once beef escalates between the Earles and The Cowboys, two of the Earpe brothers are shot, one killed. And also, a few Cowboys show up at the Earpe residence, shoot a shotgun, nobody is hit or killed, but it scares the bejeezus out of the Earp wives. And, THAT is the final straw.
He shows up to talk to Wyatt, "I heard what they did to your women. That was wrong. Want you to know it wasn't me." Ok, so he had a change of conscience and turned his back on his old ways and asks forgiveness. But, then, without any explanation, he is riding with the Earpes on their revenge quest, gunning down all of his old riding buddies like its no big thing.
Then, to top it off, he accepts an invitation to parlay with The Cowboys on their turf. The leader, Billy Broscius, calls him a traitor or something, and he looks at Billy and says, I'm his best disappointed whisper, "Least they don't go around scarin' women."
And then he thinks they're gonna just let him go back to the Earpes, but of course they murder him and sends his body back to them and one guy yells "They got McMasters" and Wyatt Earpe covers his mouth and makes a face like "God, that smells disgusting!" And that's all they ever say about Sherman McMasters haha.
For one, what was his motivation in killing people who used to be his friends, how stupid would he have to be to show up unarmed and meet with a killer that he had betrayed, and of all things, "scarin' women" is the one thing that he just cannot accept. That's the line that he refuses to cross.
My friend and I still call him Sherman McMasters when we discuss Walking Dead