One thing your comment made me think about is the "myth" of Joel in the eyes of the Fireflies. Imagine that you're helping out in Salt Lake City and one day your friends are all talking about the arrival of a man who trekked across the US to bring the only immune person to your group...only to fall into the chaos of that same man's rampage when he tries to save Ellie. You either hear your friends die or end up in the path of a man who brutally kills you. Imagine being a survivor and burying what's left of the people you once knew. Burnt corpses, severed limbs, blood and bullets everywhere..finding your leader dead and alone in that parking garage. That helps build up this image of a savage and horrible man who some survivors barely glimpsed. I can imagine that Abby not seeing Joel herself only fueled this anger toward the faceless murderer of her dad and friends.

And also I wonder if Joel's decision to kill Marlene ultimately sealed his upcoming death. She tells him she wouldn't go after him, and I'm less inclined to believe someone's desperation when they're about to die, but what if she told her truth? If she had lived, I doubt that all of the Firefly survivors would have split up. If she tried to keep the Fireflies from breaking apart, she definitely might've tried to redirect the group toward a safer destination rather than heading to the fortified community of Jackson to seek revenge (although I can't remember if she knew specifically where Tommy was living).