I tend to agree with everythng you wrote, except I think a hard coded response would be appropriate. The reason for this is that a hard coded response ensures that actions are not going unnoticed. I would not like to see a sliding scale that slowly turns someone evil or neutral or anything of that nature, but something that causes the individual to wiegh the consequences of the actions. I am not sure what a response would look like but it would have to be small and temporary but be noticable at the same time.

As for not being able to respond to all situations like this in the same manner, I think if it only trigged when a goodie landed the killing blow on another goodie it would work as desired 99.9% of the time. There are few non-intentional kills of goodie vs goodie that happen but I wouldn't have a problem with a small temp response to these as well.

The benefit of this is that the characters involved have some immediate response to the good vs good killing, this causes a RP oppurtunity for both players. And, as long as the response is both strong enough to cause pause, and not strong enough to completely inhibit goodie vs goodie action were individual RP would in some cases lead to violence at least part of the time, this would be a plus and not a negative for the game.