World pvp was supposed to be a positive side effect, but it wasn't the goal. The goal is to make low level areas feel more alive by increasing the population, so you were no longer the one dude on your server questing in Ashenvale. That goal is just as relevant for pve and pvp realms.
Aside from some issues with things like rare spawns and gathering, I like cross realm. It's nice to see people out in the world, and not just another lonely single player game.