That Edge article is pretty spot on. I'm usually more of a lone wolf player in MMOs or such, but here I find myself wanting to help and play with randoms more than usual. Nearly everyday I do some kind of good action, and surprise myself with it; today was helping a brand new level 2 player kill a sword of Crota bearer (he was prostrated behind a crate, taking pot shots at him), and let him play with the sword afterwards.
The fact that everyone in the vicinity getting credited for a kill, coupled with the loots not being shared are a great part of why everyone is willing to cooperate.