Kleps recently made a big post about why people blog, or why he blogs, or something. I think Penny-Arcade summed it up a lot more succinctly recently, seen here. We like to talk about WoW, for whatever reason, and while that's allegedly what the forums are for, those are more about whining, usually stupidly.
One of the most annoying things about the forums is the whole 'bandwagon' phenomenon. Someone says something dumb and a bunch of people repeat it as though it were true until the end of time.
One example is 'Arena is ruining PvE because blizzard balances everything around arena!' This particular attitude is annoying enough that it gets it's own post. See, this breaks down in a lot of places.
1) Blizzard has always balanced the game around PvP as well as PvE, this was true before arenas came along.
2) Up until WotLK started, there really hadn't been any case of this being true. Challenge anyone to name a change from Season 1's start till 3.0 that was made to improve arena balance and negatively affected raiding balance and... no one has ever been able to give an answer. Some try to say 'what about illumination?!' and conveniently forget that every healer was crying for illumination nerfs because paladins didn't run oom in karazhan. Some people point out stuff like reducing Cyclone's range, or nerfing Hand of Freedom, and that's assinine because those spells weren't being used in PvE (back then Cyclone even had DRs in PvE).
3) Since WotLK started, there have been some, ah, emergency nerfs to get pvp under control. Conflagrate and Arcane Barrage mainly. Most of the nerfs, like to rogues or DK cooldowns, were compensated at the same time with pve buffs, making them actually stronger in pve. I acknowledge that there have been a few times where nerfs to PvP meant undeserved nerfs to PvE since LK shipped though.
4) There have been lots of times where raiding balance has had a negative effect on pvp balance. Probably a lot more than the other way around, frankly. Lifebloom's HoT wasn't nerfed until 3.0 simply because blizzard was afraid of costing resto druids their pve viability. DKs similarly should have had their damage reduced a while ago. Divine Plea started out as overpowered as it was for holy because paladins complained that they couldn't use it at all in raids. Ret paladin damage has similarly been an issue, with exorcism going live as usable in pvp because it was needed in raids.
I just wish people would accept the fact that the game has both pvp and pve, and that you're going to see changes to game balance made for the sake of both. Sometimes, though not often, they're going to negatively affect each other. Usually, the 2 are well separated, and I expect most of the issues pvp nerfs have recently caused will be rectified in an upcoming patch (there is plenty of wiggle room in destro talents to make up the lost damage elsewhere, like empowered imp or pyroclasm).
But what it comes down to, in my opinion, is that when you demand the game be balanced totally around raiding because pvp isn't important (or vice versa) you're just being selfish. Both sides of the game are important to people, both are important to the game, and despite what idiots say, they can co-exist just fine.