I've always played on pvp servers, I kill pretty much everyone without reason.
Why? Because I can, it's fun, and when people relog to trash talk me and post about me on my server forums, well that's just icing on the cake.
Threads like these only annoy me because most players these days are whiny, self entitled LFR geared mouthbreathers (or who think they're good because they got a couple of epics in a flex/normal raid) who cry "that's unfaiiiiiir" when they get killed out in the world.
There's no rules against it, so quit complaining about it, it's always been like this.