"Hate" comes from Internet being Internet. Let's not pretend that other side isn't guilty of this, what with their "go suck Blizzard dick more" and such. Anonymity brings the worst out of many people.
Ignoring that, though, it is quite stupid to go to official forums and expect a positive reaction concerning private servers. Legally, Blizzard is in the right there, despite people twisting their words around. And even ignoring that, you go to a place where people pay money for access to a game and complain that you cannot play for free anymore. Don't be surprised that they aren't feeling sorry for your "plight". Sure, monetary aspect isn't usually THE most important thing, but it annoys plenty of people. Let's not kid ourself, a lot of PS players would never pay subscription - and I say that even though some of my guildies did start on those and eventually joined global.
Then there's the binary logic. Either you love Vanilla, or you think WoD is perfect. There's no in between in those arguments. Seeing how I still play the game, appearently I must agree with Blizzard's every decision, especially the current content drought. If I dare to speak ill of vanilla or private servers, I'm a blind fanboy - and that's the least vulgar description.
And finally, there are ridiculous comparisons. Some people are showing themselves as victims of horrible opressions - look no further than this thread. Freedom of speech, violation of human right, mentioning Gandhi in this context. This one gets to me the most. You are not some opressed minority, suffering for others who do not recognize your greatness. It's a freaking video game. On a pirate server. Maybe, *maybe* there are some people who truly believe that those are legal. But I'd expect that vast majority realized that's it's "gray area" at best, breaking the law at worst. Not a fight for freedom.