Blizzard is suing Nostalrius, a private server that hosts World of Warcraft (WoW) in its original state without any expansion packs. As one of the most popular private servers of all time, people are outraged, both Nostalrius players and retail (Blizzard’s servers) WoW players.
To understand why people are outraged, one has to understand Vanilla WoW. Writers and players far more skilled than me have struggled over the last decade to explain what made Vanilla so special. There are a variety of objective changes to the game that people can point out to be what changed World of Warcraft for them. For me, and I think a lot of other people, it is a combination.