So my thoughts were as follows: "What could Arthas possibly do to make everyone simultaneously angry and want to journey to Northrend?"
I don't know why I never thought of the answer before. What could be possibly more annoying than giving the power to grief the NPCs to the lowlifes of World of Warcraft? Arthas, you cunning, cunning man.
Some like it, some hate it, but everyone has something to say about the current Scourge Invasion, Zombie Plague, and all-you-can-take Necrotic Runes. But out of everything that this pre-Wrath event is offering, it's the Scourge "zombie" plague that's taking the forefront of the conversation.
The basic gripe comes from the fact that people can turn into zombies, spread the plague, and basically ruin everyone's day. High level players become high level zombies, and can easily decimate the low level players, even if they're on your "side." That means Alliance zombies can kill Alliance members, and can further infect Alliance NPCs and players so they turn into zombies and also spread the plague.
Players complained that there was no way for them to stay out of the event -- that they were "forced" to participate even if they didn't want to. I can sympathize with that statement, and I understand that it really ruined some people's days... but it's not like this is going to happen every day for the rest of everyone's lives. It's a temporary event that only lasted for a few days, yet everyone cries like the end is nigh.
In my opinion, the gripe is pretty legitimate. If you logged in to do your daily casual play, especially with major towns and auction houses, you were going to find yourself quickly overtaken by the plague, no matter how many Argent Healers were around to cleanse you of your ailment. You were going to find that things were made 100% more difficult by the presence of the plague.
But... then again isn't that the point of having the plague around?
We as players sometimes forget that what we're doing is living in a game world. It's made to represent a fictional, evolving story. Sometimes, that world is not going to be a perfect and safe world. Sometimes it's going to get dirty, vicious, and put us in very precarious positions. But, those positions will only serve to motivate us to find ways around them.
The whole irony of all of this is how much it coincides with Arthas's vision of Azeroth. In a fictional sense, Arthas wants Azeroth to tear itself apart through fear and self-loathing. What players did with the plague virus was exactly that. They pillaged, they turned into griefers, and they began to ruin everyone's lives without the Lich King even raising a finger.