A lot of people enjoy just the PVE content, but when it comes down to it, once you hit level 20 you could be attacked by other players in contested zones. There is a notoriety system that punishes PKers, and an honor system that rewards people for killing notorious players. Devs wanted a self-policing system.
I've been playing for 8 months and I've only been randomly PK'd 4 times. There is an immunity scroll item you can use to opt completely out of PVP for 1 hour per use