Wether or not I agree with you I'll ask these two questions. (I'd like to know the different perspectives on this)
Why shouldn't you get experience for killing people or animals? (if the amount of XP is balanced. IE a negligible amount for killing a weak passive animal)
Why should the game not treat the completion of a quest and the hypothetical fight with the quest givers as separate experience events?
For me it is a fundamental system question of if a game is giving experience per action (combat, dialogue, ect) or if it is giving experience per milestone (quest)
As D:OS is a mix of both where and why would lines be drawn as to what gives experience.
These are interesting questions. The first one seems to me, why would a skilled adventurer become more powerful, more practiced from killing a defenseless animal? Experts don't get better from doing easy things, after all.
The second question is more difficult. It can be a bit odd to, say, get experience for convincing the immaculates to let you through, and then killing them anyway. I could see it being justified that the enemies are worth LESS experience because they're off guard now, but that's hard to get across intuitively, and anyway, it doesn't really address the fundamental problem.
Maximizing XP is just something some people do, and really, most people won't bother with killing every NPC after completing their quests.
Overall, I expect there to be many situations where just killing everyone is not the ideal solution to a quest, though with the ghost component, that can make the kill everyone approach more interesting since it will open up new dialogs and possibly whole new quests and solutions.
