Originally Posted by
wolfen
Well, to be honest, My theory about Illidan's "insanity" is actually he was blindsided by his ally kael'thalas. Try to hear me out.
Kael is contacted post tft by kiljaeden, and gives him the coordinates of the Tempest Keep, and tells him he can be all powerful, but he cant let Illidan know.
Now, Illidan is prepping for the return of Kiljaeden, and needs new forces. well the dragonmaw are in the area, but they are not enough to stand against the legion in strength alone, so he uses the mannoroths blood to infuse them and make them more powerful. This makes them more ruthless, but still in order. Throughout the entire outland, besides trying to enslave the netherwing, they are pretty much defending themselves against us. Note, i am not accepting the actions they had done against the draenai in the past, but once illidan took charge, they have been on the defence since. Combating demons and us.
To further Illidan's forces, illidan "finds" or "creates" an unlimited source of arcane power, quite similar to the sunwell, but rids things of Fel Addiction. During this, he begins summoning demons enmass to his subjugation, but only to free them from their Slave Bound masters of the Burning legion (green fire quest). These new found free demons freely serve Illidan for a taste of this magic, as they are not fel corrupted anymore. Because of Illidan saving them, they combat the legion as it expands.
Illidan is not let known about the tempest keep by kael, as it would have possibly yielded allies within the draenai, through the help of akama. Illidan begins training the 5 demon hunters (quest). But at this point, Illidan begins his "insanity," Fearing what he is becoming, as whispers strike him, he seals himself atop the black temple, in the Blood elf sanctum. His commands become erratic to the point he fears the legion is everywhere, and is simply fed false intelligence. Fearing that he is betrayed by one of his allies, he never tells the Blood Elves of the true magic source he had brought them, the one he promised them other than Fel Energy.
Kael'Thalas had become Illidan's wormtongue (lotr reference), and since coming back from tft. Illidan confides in Kael, who now simply sees Illidan as a blind puppet. Never telling him of the possible allies in Shatt or Tempest keep, he begins telling illidan that there are burning legion posts where they are not(shatt), That there are possible weapons hidden around (just not in netherstorm) hence the broken digging, that bands of the Broken have begun going against him and begin serving the legion, that water was scarce and needed to help defeat the legion(Idk, the whole zangamarsh thing is just off the wall bonkers out of character for both Illidan and Vasj). kael'Thalas basically doing the legions bidding, using Illidan as a pawn to strike out at foes that have the chance to stop the Kil'jaeden's return, and making it all look like it was truly Illidan who was was causing mischief and to use him as a scapegoat to bring his true master to the world. Making Illidan into the evil one, when in reality he simply wanted to secure outland from the legion, not let them in.
Yes Illidan does brash things, he is willing to sacrifice many things for the greater good, but he is not stupid enough to enslave a race of people that helped him secure outland for themselves (the broken). He is not stupid enough to attack a city filled with civilians and the only species that hate the legion more than his own people. Illidan can be manipulated quite easily though. Hence the Skull of Guldan, hence the attack on Icecrown, and going back to try and finish the job.
The reason that this came to this point is because he is so paranoid to even leave the temple as he is being manipulated to the point he can never leave, surrounded by Kael'thalas' loyal servants, told that akama is a traitor so he does not believe him. How could this all come about? Even though Frostmourne never took his soul, it could have been closed to been stolen, possibly leaving him stable, but hearing voices(or he could have been totally fine, just didnt die, so never lost the duel?). This with the combination of paranoia of Kiljaeden coming to kill him and Kael'thalas whispering paranoid thoughts to him of such things of the Legion and the traitors, he becomes what we see, a completely out of character raid boss, who is not surprised when Akama and Maiev show up to kill him.
Kael'thalas even states that Illidan is a blind fool, when u bring the verdant sphere to shat, so I would not be surprised if he manipulated every action, to the point that everyone thinks that Illidan is so insane he has no idea what he is doing.
Just my theory on how his bc self came to be, with kaelthalas becoming the Betrayer.