Never once in Wurm was I killed by an omnicidal maniac because those DONT EXIST in those games.
I don't know about Wurm because i didnt play it more than a day or two, but i heard stories of such players in Haven&Hearth (which i didnt play for long either), and basically it seems that any open world pvp game ends up so that if you want to do anything outside of the protected zones, you need to bring a large enough group with you and disposable equipment. I'm thinking of darkfall, eve online, and xsyon.
So many things exist today because of the need to protect oneself, or ones nation. Not to mention, what would be the need of nations any more? Noone needs protecting, noones rights are going to be infringed upon. No need for government, no need for cities really even. Just small towns of people playing caveman farmville and some poor sods like me off exploring
Real life nations work because the risk is much higher for criminals : jail, death, etc...
Even with permadeath and in-game jails, people know they are playing a game and they can always roll a new character, change their IP, or whatever.
You call it caveman farmville but the game isnt out yet, we have no idea what it's going to play like, and really i can assure you that you can remove pvp and still have a fun game, take for instance ATITD and Glitch. You can also create non-violent ways for the players to compete with each other, and keep the game challenging.
Edit : oh also, about the difficulty and risk associated with player-killing, i have two counter arguments : first, the creator of First Earth specified that "hard skill" (=the skill of the actual human behind the computer) will be the most important factor, which means there would be little to no progression lost when you die, and second, in those games it's not rare to find pvp/pk characters funded by a pve/crafting alt.