Airlyn, the reason I discuss the moral/ethical choice involved in plundering is that I don't like to see other people hurt, whether it be emotionally, physically, or materially. But it seems there is a significant number of people who enjoy inflicting pain (c.f., "Plunder Progress" thread in the Forge Hall, wherein some quote "whiners"). If plunderers stole only from other plunderers or those who assented to the practice, there would be no problem. Of course, folks should be aware that plundering can occur, but, likewise, no plunderer should be shocked when some victims despise what he/she has done. Personally, I don't worry much about my city being plundered, although I disagree with the practice.
I guess my aversion to harming others stems from my childhood. I hurt someone very badly, I can still see the pool of blood and him being carried away on a stretcher. I vowed to never willingly physically harm anyone again. When I learned of other types of pain, I extended my vow to cover them as well.
@gutmeister -- There is no set exchange rate in this game, though a conventional rate exists; so, no, it's not a question of morality.