The key issues with psychopathy being lack of empathy and utter selfishness, I suppose there's no reason why these people can't be made to understand why it's in their best interest to play nice. After all, many of them do now.

The bigger question for me is the matter of defensive force. If I catch a murderer in action, but by the time I pull out my gun, the deed is done, am I obliged by morality to refrain from killing him? The defensive opportunity being lost, am I now in a new category of moral obligation?

I can see how it is so, since rehabilitation is possible. What we're saying here is that there is no just punishment; there is only restitution. I can't find any ground to debate this point, given my current moral understanding, so I suppose I'm bound by it...

It's a bit of a tough pill to swallow when considering this scenario of a mere instant between justifiable homicide and murder. Then again, whether a minute or a year, revenge is not defense. So there we have it, I suppose.