Yeah its simply way to easy to inflict serious dmg with the PK.
Whenever a "good" player fights a "bad" player that has any other weapon than the PK, the good player can actually kill him without loosing too much shield and hp due to his superior movement, aiming and map awareness.  But a "bad" player with a PK has so much greater chance to even kill the good player, simply because you only need one "lucky" millisecond of line of sight and you can hip fire away 160 dmg. 
So even if a good player will more often than not win against a bad players with a PK anyways, it still decreases the skill cap of this game and in my opinion actually ruins the game when hordes of noobs just jump in on you with PKs because they know thats their best chance of killing you.