This would have pissed me off.
Perhaps I'm one of the 'care-bear' players that were so warmly talked about, but would you like to name any online sandbox world where you can't be routinely screwed over by some resident moron? Hundreds and hundreds of MMO's out there and every single one chants 'PvP' like some other zombies.
Maybe, when they manage to eliminate balance issues, lag issues, key macros, bug issues from the PvP areas, then I'll really enjoy them. Things like TF2 I love.
But if I'm playing to relax, taking in easy routes that get me little risk and some idiot repeatedly drops the world ending on me; I'm really gonna get pissed and stop playing.
However...
World's shouldn't be static. Unpredictability makes it more exciting. But you can't rely on Players to provide that unpredictability because, in general, we're a bunch of bullies. Look at how much advantages we take over even the easiest fight...what makes you think we wouldn't use the same devious sneak tactics in a PVP fight?
Now if you want to use that, take it further...have the Undead Presence creep slowly across the land...so the care-bears can huddle in their cities whilst the risk-takers leap onto the front lines, but then get butchered by the risk takers coming forward. Have Zombie artefacts spawning within the no-man's land, so they turn on each other. Really turn it into the Day of the Dead.
Don't just go, "Ooh it's Halloween, here's something that will annoy all but benefit a few."