Remember the Defias Brotherhood? They were thieves. If they lived on Earth we would attempt as much as possible to capture them to face justice, and things like the death penalty wouldn't even be on the table. On Azeroth? The local law hires adventurers/mercs to clear them out with swords in the gut. We basically assassinated the entire faction, and the only person we ever saw them actually kill was Tiffen, which could be called an accident since it was someone in a crowd throwing a rock at Varian. All the farmers in Westfall were just being scared out of the area, so we never saw any of them get murdered (at least, not until the new Defias Brotherhood in Cataclysm, but that can be considered a different group), and yet we go to great lengths to kill all of them. The few Stormwind did capture? We kill them when the riot in the Stockades.
I mean think about it. Our characters will kill ANYONE as long as someone is paying them or get something from them. What is moral about that?