It's very confusing when you most of the time questing amongst peacefull players. Then suddenly one goes nuts and attacks on you. Following this logic, if you wanna stay alive, you must always attack first on every Horde, kill on sight lol. Crazy game.
Personally, i never do first blood if not reason for, BG's satisfy the need for me. I have better things to do and it just makes my progress slower. These backstabbers most likely get their kill. Advantage of very twisted startle, all cd's burned for one burst lol. Same guys never visit battlegrounds, and are 90% PvE oriented players. Often in group. Later i hunt them down few times ofc. Keep "Kill list" and share it for others? :D
It's as crazy as if you irl shopping at the mall and suddenly some nutcase hits with the shovel at your face.
World PvP is not griefing and ganking, it's not lowbies slaughter-fest either.
All above are only mental features, personal disorder-alike-symptoms imo :P