The new Fallout games under Bethesda are chock full of karmic choices, stat-based dialogue options, and neat little bypasses that can cut out a huge portion of their respective games, barring 4 and 76. However, this is something that was pioneered by the original, top-down, isometric, turn-based entries. What's more, there was so much more potential in the stats you picked early on - in fact, speech played such an impactful role that it could even be used to take down the final boss singlehandedly, bloodshed averted, in the very first game.
With an intelligence stat of at least eight and a high speech skill alongside the Smooth Talker perk and, perhaps, some mentats in toe to get yourself into the charismatic, slick speaking groove, you can convince the Master to kill themselves. What's more, you can avoid transforming the cathedral from an ominous post-apocalyptic breeding ground for cultists into a plasma-blast firing range just by donning their robes, so perhaps some stealth would go a long way too.
To convince this villainous big bad hell-bent on world domination to kick their own bucket, you have to debate their plan for the Unity. "Do you join the Unity... or do you die here? Join! Die! Join! Die!" the Master screeches, to which the Vaultdweller can demand that the Master prove their plans to be true. This of course enrages the Dalek-looking monstrosity, "I don't have to prove anything to you!" Prod harder, though, and they say, "The Unity will bring about the master race. One able to survive, or even thrive, in the wasteland. As long as there are differences, we will tear ourselves apart fighting each other. We need one race. One goal."
A very on the nose jab at racism and white supremacy - the Master's ultimate goal, like with the Daleks (this entire ordeal is very Doctor Who), is to eradicate all other life and bring about a singular, superior mutant race. The Daleks too spawned from a post-apocalyptic dystopia riddled with radiation and in-fighting. Maybe it's a coincidence, but I can't help but hope that Obsidian was in part inspired by the hit BBC sci-fi. Now, you can make fun of his looks, call him a bigot, and generally push his buttons, but that's not advised - you have to keep the Master level-headed, talking, ego spilling.
"You've got a problem with your master race," the Vaultdweller reveals. "And what is that?" the Master inquisitively responds. "I happen to know that your mutants are sterile." The bombshell is dropped, the Master loses it, devolves into a fit of rage, "Preposterous! The FEV-2 virus doesn't destroy the reproductive organs of those it mutates," he cries. He even goes as far as to call the document you provide forgery, a deceptive trick, a ploy to undo his plans through conversation and debate, but it's no fake, and he slowly begins to realize that cold, hard fact. "It cannot be. This would mean that all my work has been for nothing. Everything that I have tried to... a failure! It can't be!"
The Master realizes the horror of what he has subjected the wasteland to, "It was madness. I can see that now. There is no hope." The dialogue window closes, and the Master swiftly starts the procedure to blow up the church, killing himself and all of his followers. A timer begins, and it's up to you to get out of dodge. That's it, a few clicks, some interesting revelations, and a slowly unraveling villain realizing their mistakes, their failures, and the ultimate pointlessness of their whole plan.
They don't devolve into the destruction of all who wronged them - they take themselves out, saving you the effort, the bullets, and the many healing items you'd no doubt be wasting. It's a nice break from the typical ending of a game such as this, one where it all comes to a head with a gargantuan crossfire of rapid-fire bullets and blood spewing out of newly opened orifices. Perhaps, going forward, Fallout can find its footing and return to these roots, bring back karma, and up the potential in charismatic smooth talkers, because right now, the series really hammers in combat, but what about us folk who just want to try out some pacifism for a change?