Perhap's that's it, I don't go around killing just anybody on a whim, I only do it when required in a quest. I have read a LOT fof posts from people who will kill someone simply because they felt like it, or the NPC does something to annoy them (Like Nazeem and his class snobbery) I won't do that, not out of a sense of moral superiority, but because I really can't be sure of how it might affect the game. It seems too much of a risk to take for a few moments of slaughtery fun. I may do that at some point, just go around killing anyone I meet just for fun, but that will be at the point I am probably done with the game and want to go out in an evil blaze of glory. (TBH, I may not bother even then)
I guess I'm just old enough to know that there are a$$hats in real life who say stuff and you don't kill them. Nazeem? Yes, I've met people like that. I avoid people like that. The elf at the stable "Horses horses horses all day. Do you know how dull horses are?" .... yes I do. I owned four of them. Nice animals, but they're a lot of work. I sympathize. That Nord butthead in Windhelm who picks on the Dunmer? I picked a fight with him in the Dunmer pub and one punched him. Now he's like "let's get a drink" and the Dunmer merchants give me better prices.
Also I don't kill them not out of "moral superiority" but simply because I can't be bothered. It's not worth it. Like I've posted elsewhere I've been accosted while traveling between towns by the random Orc, or random Redguard who uses the typical insult and used the "I"m sorry. I should go." response simply because I knew I could kick their sorry a** all the way back to Hammerfell or wherever they came from, unless I decided I was close to leveling up and needed to work on my blocking skills a bit in which case the fight could last 20 minutes or until I got the "level up" sound whichever came first. Then "you shouldn't talk like that to me." Most of the time I look at it as a pain -- now I've got to loot the corpse... oh whoopie another flawless diamond, and wow look at this... another daedric sword to sell... if I take all of this crap I won't be able to run, and there aren't enough vendors in Skyrim to cover the value.... take the gems, gold, arrows if any and leave the rest.
I'm on a 360. I've gone through this quest twice and it fired perfectly both times. AND the DB Muiri's Quest was active at the same time. You have to play Columbo with this one. The trick is in the detalis.