PK activity have been known through many MMORPGs for years. Game that apply PK System intend to make the game have more real environment, more user interaction in game. A PKer killing someone and the other player will kill the PKer to revenge or gain some bounty from him/her. They are called PKKer (Player Killing Killer)
There are so many reason to doing PK. Like train spot take over, KSing (Kill Stealing), In game popularity 
, or even such as a high conspiracy to break releationship between in game community like Guild, Clan, Tribe, Union or whatever we called it.
Speaking with Is PKing Good or Evil, depend of how the player using PK System. If they evil side motivating them, then it'll be Evil and so vice versa. PK System can kill some player desire to play and then leave the game, but for they that like challenging one this situation motivate them to be more strong enough and defeat the PKers 
.
So now... how do u think guys about PK? No Flame, No Offence... Feel Free To Comment 
Peace!!!
