In most games, I've always been against open PvP. I know this comes from my experiences on a PvP server in WoW- I was expecting fun raids on each other's cities and such, and got plenty of that- but more than anything else, I saw high level players going back and harassing low levels who couldn't fight back- with no consequences! After a while, I just switched to a normal server and avoided PvP entirely in MMO's.
However, having read all of the blogs for Pathfinder Online, I'm a lot more optimistic about it's PvP and am looking forward to participating! With a levelless system, there shouldn't be situations where you just can't fight back (unless you're completely outnumbered- but even then, it's just another reason to team up, unlike other games where even big teams of players are effectively ants to a higher level). And there are major consequences for people who just kill indiscriminately. With territory battles and other directed systems, it really looks fun!