People roar about anything WotC produces, says, or does.
This is the internet and we would roar if WotC suggested the M-U should use d6 for hit points.
People would roar if Forgotten Realms was announced as the new 'core' setting for DnD and they'd roar if Forgotten Realms wasn't announced as the new 'core' setting.
Why do you think even the most basic polls from WotC now have Option A, Option B, and Option 'I will tell you what I want'.
Personally, I was pretty surprised that there would be any complaint on the idea of colorful details in the core book related to Wizards.
There has to have been over a hundred different mage guilds that WotC and TSR have produced in products and magazines and ezines over the 30 years of the game. Most of the prestige wizard classes had fluff text that mentioned magical orders and many campaign and splat books are filled with descriptions of magical orders.
The only real problem with guilds and orders for mages and sorcerers is really deciding which ones your players are going to include in some sort of back history or background.
The same really goes for Rangers, Paladins, Fighters, Rogues/Thieves/Assassins, Scouts, Knights, Cavaliers, and pretty much any class in the game. The material is there to be used.