D3 was designed from the ground up with no focus on PvP. They were going to have an arena that you could brawl in but it was to be unbalanced and there was no emphasis on esports. I think they eventually added the mode but I don't know anyone that took part in it.
I personally think PKing is stupid, but at least in D2 you can make private games and thus avoid it. I am doubtful they'd introduce a system of that nature without a toggle in an open world system.