What has happened to this game? You've played since the beginning, myself since about 6 months post-launch and at no time prior to TBC do I ever remember such Class Warfare between what is essentially the same demographic. I've been a raider, I'm a "casual" now and have been sometimes in between but the game now generates much angst within the community and unlike pre-TBC where it was directed at Devs (in the form of "nerf this" and "buff that" cries) it is now directed between players.I think the class warfare between casuals and hardcore is older than that, it dates back to the first guilds defining themselves as "raiding guilds". What TBC added to that what the devs themselves infamously called "welfare epics", and then lazily proceeded to use the same armor models for. That made obvious a fact that more rational people knew all along: That raiding isn't in any way "superior" to other modes of gameplay. In the perception of the general population raiders moved from being the guys in the awesome gear everyone wanted to have to just people who played the game in a different way, grace to having more available time. The lack of mutual respect comes from the two groups having very little contact with each other, sometimes even if they are in the same guild. The casuals are dismissed by the raiders of being no use to them, because they don't have the hours of wipe experience for each boss that teaches you how to beat them, nor the right kind of gear. Meanwhile the raiders are of no use to the casuals either, because the raiders are so busy with their raids and their farming stuff to finance raids that they never have the time to play in a casual group, nor do they have the desire.
If there is a negative change in WoW since the launch of TBC, it really boils down to the fact that Blizzard's design choices have pitted players against each other. A series of negative cascading effects has led us to the point where there are now 2 distinct groups of players and they, for all intents and purposes, DO NOT like each other. Worse yet, there is a genuine lack of mutual respect between the players in the community.
In hindsight, the fact that in pre-TBC, non-raiders got rolled in PvP by raiders due to the gear inquality, there was never this level of anger and venom on display. Sad that a game I have enjoyed for so long has devolved into this.
The increasing acrimony is probably just an effect of burnout. MMORPGs are curious in that many people don't stop playing when they stop having fun; instead they keep playing with a more and more negative attitude, complaining all the time on the official forums. And as Ontherocks remarks, the negativity is directed badly at other players. Not only casuals vs. hardcore, but also mages fighting warlocks, or other classes crying for somebody else to be nerfed. It is an illusion that you could have more fun if only fun was taken away from somebody else. World of Warcraft certainly has balancing problems, but these are more due to the impossibility of balancing classes in a way that they are equivalent but different in solo play, group play, and all the various forms of PvP.
But the real culprit is game design. The separation of raiders from casuals stems directly from the arms race between developers and top raiders, in which the devs try to create harder and harder content, and the players try to beat it. They do succeed at beating it, but only at the price of getting completely separated from the rest of the population. Meanwhile even the easiest raid dungeon is designed to be too hard for a pickup group of casual players, which only increases the resentment between casuals and raiders.
I still believe that the arms race should be stopped, that raiding should be made a lot easier and a lot more accessible for a much wider part of the population. It is only World of Warcraft where the casual do PvP and the hardcore do PvE, in all other games it is the other way around. PvP is a lot easier to use as occupation for the hardcore, because it scales itself: you measure yourself directly against the other hardcore players, and not against content designed by devs. Ideally every part of the player base should have access to all parts of the game, play a bit of everything, with a preference for whatever suits you most. The current system in WoW where you basically specialize in one form of gameplay and can't easily switch to another form is harmful.