Allow me to give you an academic answer:
Why Did Players Kill Illidan in The Burning Crusade?
At the time, Blizzard framed Illidan as a “mad tyrant” ruling over Outland. The reasoning given to players was:
- Illidan Was Dangerous & Unstable – He ruled Outland with an iron fist, and his forces (the Illidari, naga, and fel orcs) were seen as a growing threat.
- Shattrath’s Army Declared Him an Enemy – The naaru-backed Sha’tar (with the Aldor and Scryers) portrayed Illidan as a villain who had to be overthrown.
- The Betrayal of Kael’thas – Kael’thas Sunstrider, who originally allied with Illidan, defected to Kil’jaeden, which made it seem like all of Illidan’s allies were now in league with the Legion.
- Illidan’s Growing Paranoia – He wasn’t directly attacking Azeroth, but his increasingly erratic and isolated rule made him seem like another power-hungry warlord.
At the time, the Burning Crusade storyline didn’t actually confirm whether Illidan was truly evil or if he had secretly been working against the Legion. So from a player perspective, we were just following orders from the Sha’tar, Maiev Shadowsong, and the factions that sent us to kill him.
The Big Retcon in Legion: Blizzard Fixes the Mistake
By Legion, Blizzard revealed the truth: Illidan was never the bad guy. Instead: 
He was secretly building a resistance against the Legion, using Outland as a staging ground.
He had been training the Demon Hunters (Illidari) to prepare for the inevitable invasion of Azeroth.
Kael’thas, not Illidan, was the true traitor, but by the time the players got involved, Illidan had already been falsely framed as an enemy by the Sha’tar, Maiev, and others.
Essentially, The Burning Crusade was a blip in the lore, and Legion had to reverse-engineer a justification for why players had been tricked into killing one of Azeroth’s greatest defenders.
Would Outland Have Been a Threat If Left Alone?
Probably not—at least not in the way The Burning Crusade originally framed it.
Had Outland been left alone:
- Kael’thas would still have betrayed Illidan and tried to bring Kil’jaeden through the Sunwell.
- Illidan would have fought against Kael’thas instead of the players doing it.
- The Legion would still eventually invade Azeroth, but this could have been a later expansion where players aid Illidan instead of kill him.
This is exactly why Legion had to fix the mistake, bringing Illidan back as a hero and retconning TBC as a misunderstanding fueled by faction politics and manipulation.
Did Blizzard Retcon the Mistake from WoD Through Shadowlands?
Yes, Blizzard spent years correcting the consequences of The Burning Crusade’s story mistakes by:
- Warlords of Draenor (WoD) – Revisiting Draenor’s past and exploring orc and Legion history.
- Legion – Bringing back Illidan and revealing that players were wrong to kill him.
- Shadowlands – Confirming that Illidan’s soul wasn’t in the Shadowlands because he never truly died. His fate was intended to be different all along.
Edit: For clarity and accuracy.
Conclusion: Was The Burning Crusade a Blip in the Lore?
Yes, Burning Crusade forced a lore mistake where players fought Illidan instead of helping him.
Blizzard retconned it in Legion, admitting Illidan was never the real threat.
If left alone, Illidan vs. Kael’thas could have been a setup for an expansion where we fight alongside Illidan instead of against him.
Essentially, TBC wasn’t well thought out, and Blizzard had to spend years fixing it. If TBC had been written differently, we might have gotten a better version of Outland’s story that led directly into Legion without needing all the retcons.
Thank you ChatGPT for confirming all the facts here. 
