When spurned, a self-righteous hero can become a villain.
Some time ago I was running a gritty post-apocalypse campaign. One of the players ran Larry, a manipulative, conniving character who had a profound sense of loyalty to the fellow PCs. He would do anything for his in-group, but he was also deeply skeptical of anyone else, to the point of paranoia. To make things even more difficult, Larry was self-righteous about his paranoia. “Guys, I’m doing this for you. You’re so naive, and without me to protect you, you’d all die,” was his common response after he would derail a negotiation or start a fight with strangers.
The thing is, he was a very capable character who on several occasions really did save everyone else from premature death. In other words, the positive characteristic of loyalty was deeply intertwined with the negative characteristic of paranoia. As the story and the character evolved, it became obvious that Larry was becoming more and more of a liability to the group because of this self-righteous paranoia.
We collectively decided that the character could continue down this path, but that we’d also all be OK with a player vs. character situation if it came to that. The player was fine with bringing a new character in to replace the original if necessary.
The situation came to a head when the group was in a makeshift survivor settlement, gleaning information from some NPCs, and Larry started essentially interrogating one of the NPCs. Knowing that they were surrounded, one of the other PCs pointed a shotgun at him and demanded that he let the NPC go. Fueled by self-righteousness and anger at the perceived weakness of his colleagues, Larry refused. The other PC shot him in the face. Larry lived, but ran off.
The player created a new character to replace Larry, and they all figured that was the end. But as I thought about I realized that Larry would be a perfect NPC villain. He knew what he’d done was right. He was the only one in this small, desperate band who would do what was truly necessary for the survival of the group. He’d saved their hides on multiple occasion. And what was his reward? They almost killed him!
I determined that Larry would follow them at a distance and use his social manipulation skills to spread word that this group didn’t operate in good faith, that they were nothing but marauders. Ultimately he faced them in an epic showdown. It was fantastic, in part because the PCs felt guilty for what they’d done to Larry, even though they knew they’d had to do it.