DAoC which was lauded for years as the best large scale PvP MMO, tried a PK server... guess what, it was the first server to be officially shut down. There was a rush of people to it when it launched, then after a few hundred people got to max lvl, they'd spend their time camping new player areas, and PK'ing new people to server till they left, making it nigh impossible to join the server community (they didn't want "scrubs" tainting their server).
The established community started to drastically fall in population as the vets started to eventually leave, which dwindled the amount of PK'ing, which caused more people to leave, and the PK'ing dropped even more, so on and so forth. Till eventually population dropped so low that even with the added 300% xp bonus to lvl'ing as incentive to try the server, new people wouldn't join because the server was always dead.
This was in a PvP centric MMO, now imagine how bad it'd be in a PvE focused one like XIV.