Night elves at 10 000 years ago practice magic daily and it isnt forbidden. Even their queen Azshara and her highborne are strong magic users. Malfurion never hated his brother but as someone who has high position in the NE elves society he has to do what he has to when they found out about Illidan's betrayal thus he is know as the betrayer. The others wanted to kill Illidan but he persuaded them to imprison him and spare his life.

Illidan sought power because he was jealous in Malfurion. Illidan practice magic while Malfurion practice druidism taught by Cenarius. He didnt expect druidism to be better than magic when he took the path of magic and decline druidism and so he sought power from the Burning Legion and also to win Tyrande's heart as he thought Tyrande thinks that Malfurion is stronger than Illidan. Soon after he gain the eyes from Sargeras he betrayed the Burning Legion and helped Malfurion to defeat them. That is why he is blind as in order to receive the gift from Sargeras he has to have his eyes burnt to be replaced.

L2LORE before you speak

I've read all the Warcraft novels except for Rise of the Horde which just released in Malaysia recently i think. You mentioned magic is forbidden but it isnt so there....

He betrayed his people by swearing allegiance to Sargeras after Xavius corrupted him. Magic was only forbidden after the portal was closed which is where Brox the orc sacrificed himself to buy time for Malfurion and Illidan to close the Burning Legion portal. Magic isnt forbidden before the invasion of Burning Legion. Even the night elves used magic to fight the legion. Illidan is the most capable magic user among the night elves and he wielded superior magic after Rhonin became his tutor sort of.

If he wasnt in league with the ligion till he consumed the skull of Guldan then explain why he is blindfolded? Look at War of the Ancients book 3. Illidan face is printed in the front page and he is blindfolded. He didnt want to obey Sargeras but in order to defeat the legion he swore allegiance to Sargeras because he believe magic is the way to win the war therefore he had to pretend serve Sargeras and learn their dark arts of magic. Illidan once mentioned how magnificient and strong the dreadlords are to be capable to wield magic to raise an undead army and he too wanted that power.

If you still dont believe he used to help the legion then explain why did he bring the Demon Disk from Neltharion or known as Blackwing in WoW to Sargeras? He wanted his trust so he had to betray his brother and Rhonin in order to get the disk and present it to Sargeras.

Seen has explained it earlier than me

now, enough lore, YOU, L2LORE.

Arthas is the biggest tragedy in Alliance Killed his own father and his mentor, Uther

That wasnt his actual plan i think. It was Brox and Malfurion who helped Illidan closed to portal as well as the aspects leader themselves. Illidan wanted to close it himself but i doubt it will be successful

So actually he got lucky when his brother and gang arrived to save the day. He even endangered Tyrande in his plan so i think he has allegiance with the legion. He brought the disk to Sargeras which is a big help to Sargeras but if he didnt then the disk will end up in Alexstrasza and Ysera and with that they will be able to restore their power and win the legion after dealing with Blackwing

Lol sorry i misread what you meant. I had to read the 2nd time to get it. Still he wasnt banished for his magic use but was imprison for the well he created. He pretended but then he risked other people lives in order to gain Sargeras trust. If you were to say like this, then he didnt serve legion and didnt help the elves as he was only trying to gain power for himself. He did not care about the lives of his subordinates when he drew magic from them

Sorry again for replying without understand fully what you meant but i get annoyed when i see Malaysian trying to act as a foreigner and do all the leet talk. You know how annoying those leet talk are ingame

My friend told me there was a novel which talks about the Paladin order but then he cant buy it cause they only willing to sell to him in a Package which contains 3 other books(Last Guardian, Cycle of Hatred and Day of the Dragon) which he already own. No point paying so much just for that book

So maybe that book about the Paladin order has some story to do with Arthas and his betrayal