"Accidental mail-out to random, random passes it along to friend. Friend then one-shots most of Ulduar and gets abusive when found out and banned. Seems self-explanatory."

How do you accidentally mail a GM item? This is the ONLY time in 5 years of WoW I've heard of where a GM item was mailed to a player, so obviously "accidents" like this don't happen that often. But Blizzard never said a word, so we don't even know if the GM who did it so much as got a stern warning. An entire guild got banned(at least temporarily), and we don't even know what happened to the GM who gave out the item that indirectly caused said guild ban.

Sure the item says "Cheater", but there's lots of flavor text like that. One quest in the game(in Burning Steppes) says "You know this because you are psychic". Do you take that text at face value too? Every player that does that quest should setup a psychic hotline(or repent because Christians believe psychics use Satan's power)? Hell no, because WoW has tons of hyperbolic flavor text like that.

If a kid's parent gives him a gun, and the kid uses it, do you completely pretend the parents weren't at fault at all? Maybe it was an accident, maybe it only happened once, but it caused damage. You have to give blame to the parents for giving the kid the gun, without which he couldn't have committed his crimes. If you go by the Blizzard approach, the parents would/should have grounded the kid for life and pretended nothing happened, while ignoring any fault they themselves may have had.