An Interface for Evil

Matt Mihaly recently dicussed the difficulty of making the enemy obviously bad without resorting to making the enemy stereotypically bad, which prompted Brian Green to muse on the nature of evil. After several rereadings, I'm still a little bit lost. I just don't see a problem at all. In many modern games, the user interface itself conveys plenty of information about the status of mobs via clear indicators such as label color (red ones are aggressive, yellow ones are passive, green ones are friendly), mouse-over cursor changes (cursor becomes a sword, cursor remains an arrow, cursor becomes a smiley face) and floating icons. The fact that the mob belongs to a usually-evil/hostile/bad species or faction doesn't in any way prevent the user interface from presenting the player with the appropriate set of interaction affordances.

Or maybe they aren't asking about how to implement unexpected interactions with mobs. Maybe they are really asking how to get the player to want to react against type. How do you make the player hug the ugly girl or stab the pretty boy?