This would be perfectly okay if,
Each kill gave 75XP and the talking your way out of it was 300XP.
Guy who gives no shits kills all three. Gets 225 XP
Guy who thinks, maybe there is a way out of this and works for it gets 300XP.
Guy who thinks, I'm suave enough to talk my way out of this, succeeds and gets 300XP, then decides he likes the one of the guys bling and kills them for it. 525XP.
Your solution does not solve the problem at hand. I noticed in your other post that you dismissed it, but I feel that the issue does hurt immersion, as a "right" way of playing is emphasized. After all, if there is literally no downside to killing everyone afterwards, then you are just hurting yourself by not doing it. It's like having a really overpowered thing in the game; sure, you could just not do it, but what of your friends? Especially other players in public groups.
Additionally, what if you want to compare experiences? If you did not perform well because you ignored the optimal route, then it's your fault. The player is directly to blame for not using all the resources available. And if you did perform optimally, despite intentionally hindering yourself, then that's that. But people do struggle with the game, including my friends, and as such are motivated to do the most prudent thing: kill all of the silent monks, slaughter the civilians, and prune the merchants we don't need anymore. Not everyone is a murder hobo, and not everyone wants to play that way. And in a group where everyone has free will, all it takes is one guy to mess it up for everyone.
Tl;dr does not solve the problem, which hurts immersion and detracts from the experience as a whole.
