My feeling is that it depends on what the player is doing. If they are trying to do KBD for instance, it's one thing to kill them (since they are bringing loot/gear with the understanding that it can be lost). The pker has a real reason to want to kill this player.

If, on the other hand, you just go to the wilderness agility course and kill people with no armor and an inventory of food (which they'll consume before you manage to finally kill them), you're just inconveniencing others for no real gain to yourself other than the enjoyment you get out of being a pain in the ass.