Right - if you were somehow sneaking around with the other characters picking off enemies without the enemy in dialogue being able to see or hear what was happening in a real game-world sense, it would be fine. But "locking" one enemy into dialogue with one character, then killing the enemy's buddies right next to him/her without the enemy reacting is both a silly exploit and (to break out the cliche) immersion-breaking. I'm not aware of any other RPG that allows for this kind of thing, and for good reason.
