It seems that in Treasure Vault, the Pacifying rune was copy-pasted out of Agents of Edgewatch while forgetting that in that AP, the PCs are expected to be dealing nonlethal damage all the time.
So with the Treasure Vault version you can stab someone to death with a weapon that makes them feel horribly guilty about stabbing you back.
Well, that was available even in Edgewatch. You aren't required to deal non-lethal damage in that AP. You just have that option without any penalties.
Also, the -2 it gives is untyped and lasts an effective 10 rounds, so could multiple party members with Pacifying weapons stack up a huge penalty on an opponent's lethal attacks?
Apparently, yes.
Probably best to not run the game that way. It should have a type for the penalty - probably Status. Though the enemy can avoid all of the penalties if they just deal non-lethal damage themselves. But that is harder to do when not in Edgewatch.
It would be broken to allow it to stack from multiple weapons/party members. And we have the rule that says if it's too good to be true, it probably is. So I think it's obvious we shouldn't let it stack.
But there probably also needs to be a requirement of dealing non-lethal damage to use the pacifying rune.