yea, i must admit, seeing a massive battle on a mmorpg would be very impressive to see,but think of the reality, not everyone is in a guild, what would they do if they wanted the special robes, which your guild has held captive?? it would suck for them. Player killing really on causes problems, unless ofcourse there is a special arena created for those who want to player kill,  but walking around being able to kill another player would not be great at all.