I think the part of this thread that frustrates me the most is all the times i have been ASKED to come in and help with certain mobs, because people need the drops but truly understand that they simply cannot do it themselves. In these cases I usually try and bring my shammy and cleric for buffs and heals and let the newer layers "do it themselves" but sometimes i tank my way thru to get it done. Also because the Headhunter quest requires you to go to these zones i know that it also makes it much more difficult for newer players. I have been on the other end so I always try and be respectful of other players.
I understand that not everyone plays that way. Not all higher end people are @$$es. Many, many, many of us assist in mobs for the epic weapons quests, specific named mobs for loot, and when newer members are screaming for help from getting mass assaulted by high end mobs (Karnors). I have assisted in hundreds of 1.5 mobs for people and haven't had any reason to go near those mobs other than to assist others.
As leader of <PROGENY> i simply ask that if any of my members have KSed or mob jumped in lower levels, please PM me or send me a tell in game. I will take care of it. I recommend that you try that for all guilded members. The only other thing i recommend, and i have had this happen before, is simply send a tell to a player or even a shout when in zone that you are going after a specific mob and please do not kill it. That way when someone does you can show that you tried to let everyone know. I have received tells like that and have offered to assist rather than ks. I explained what i was after and we were able to meet 1/2 way. Many times i simply left and came back at another time.