This thread confirms what I've long believed.
When Sunset Invasion came out, the reason so many people got upset wasn't because it was a fantasy scenario ruining their historical game. They were mad that Paradox had made this DLC instead of the Republics or Theocracy DLC they were demanding. Which is why most of the complaining was that Paradox was "wasting resources" that should have been better spent on something else -- the thing they wanted.
Then, once the revolt started it became the cool thing to say -- that you hated SI. So a lot of people just joined the haters club without really thinking about it or playing it. Which is now put to the test when they see the Zombie thing, think it's cool, and have to deal with the fact that it conflicts with all the nonsense they've been repeating for months without thinking it through.
It was never really about fantasy DLCs and history. It was about a small group of people who were acting out when they didn't get the toy they wanted first, who then infected the whole argument. That was how it always seemed to me at the time, and it's the only explanation how all those arguments they made disappear when the next cool fantasy DLC idea comes out.
For the record, not a particular fan of zombies but looks fun. Hope they actually do it. It would be a great way to watch your carefully built New Roman Empire fall apart.