All of the above are true (perhaps) when you look at it from your perspective. Now look at it from mine: I'm next to you. I'm slaying. Before I kill my first mob but after I've attacked it, you come out with an MC or and AOE and take the kill. I'll say it's inadvetent. It happens again, and again, and again and ... like I said. See it from my perspective. Even innocently you can have a negative affect on my game. If you're not innocent you can just ruin it. One player on every world doing that in just one spot will cause a lot of bad feeling and more and ... nothing will be done about it apart from the person who should be punished is probably (in effect) being rewarded for their antisocial behaviour by being the one that gets the kills, the drops, has 'fun' etc. 'nuff said.
