RangerWickett said:
And consider carefully before you go saying that this would itself be evil. If 'evil' means that you're a killer (which the D&D core rules description of alignment seems to suggest), then this method is similar to either good police work (to find criminals and punish them), or psychological examination (to find potential criminals and rehabilitate them before they hurt someone). And that's something we can all get behind.
It seems in this example, you focused on the "killing others" but ignored the "hurting, oppressing" part. This goes back to the bar keep who maybe smacks his staff around a bit. Maybe he's just tyrannical in boss status. Doesn't hurt them but oppresses them - bad hours, ill wages, etc. Evil? Possibly. Smite worthy? Probably not. Quite probably not even criminal investigation or charge worthy.
What about the bouncer at the bar? His job is to ensure the establishment remains orderly - this sometimes requires hurting others. What if he likes it? What if that's why he took the job? He wanted a legal way to smack others around. Perfectly legal job - still, he might be evil. Again, not auto-detect-smite worthy.
It's just not as simple as you would have it in your example, or as Frank the DM would have it in his games. At least not IMO. This is one of those issues that, more than most, is something that seems to fall on the DM's shoulders - he has to decide how and what is evil in his games, and then try to explain that to the players, so as to avoid future DE mishaps. I have to say, if I played a paladin in a game where simply detecting as evil gave me the right to smite - my character's name would be Smitey Smiterson.
Or I'd play some sort of con artist who tried to convince people he was a paladin, and make them give up cash and women or be smote for haveing detected as evil. Small communities only. No big places where it could be easily verified or not.
And, no, finding potential criminals in order to rehabilitate them before they do something isn't something we can all get behind. See warning signs and try to get them help? Yes. But what you said doesn't imply that. What you said is a little too thought crimey for my tastes. And I think it would be for a good portion of the actually-Good societies in a game (using the standard D&D setting/modern morality).