The event was added to cause chaos but zombies don't do any damage so why would they be KOS? There's really no incentive to kill them. The goal is to get infected as fast as possible and infect as many people as you can. (you can infect yourself by smashing a pumpkin). The goal of the event is to earn XP, cash, and potentially a lootbox for infecting other players, you get absolutely nothing for killing them. If you want to kill them, I can have it do damage so it's justified but there's really no reason not to participate unless you're in your base or something which is totally cool too. I added a chance to get a pet and chat tag and increased the rewards by 4x for infecting players.