Kael gets a bit of a bad rap. Of course he was nuts by the time Tempest Keep (and Magisters’ Terrace) rolled around, and to tell the truth he was more than a little misguided by the end of WCIII: The Frozen Throne. But up until that point I maintain that he did nothing wrong.
So let’s talk about Kael. He was in Dalaran – and had been for several decades, at least – when Quel’Thalas (and his dad, King Anasterian) fell to the Scourge. He rushed to his homeland’s aid as soon as he was able to, and immediately set about fixing things. He destroyed the Sunwell, but only because the corrupted Sunwell – which had been tainted by Arthas’s act of tossing Kel’Thuzad’s skeleton in it – would corrupt and probably eventually kill the elves. He had no idea that destroying the Sunwell would cause another problem to arise – his race’s addiction to its arcane magic.
Angry, sick, and upset, the elves turned to the Alliance, who they had been allied with previously during the Second War. Unfortunately the Alliance was not particularly interested in working with the elves. You can thank a racist buttlord named Garithos for getting that partiuclar ball rolling. He forced the newly-christened blood elves into what were essentially suicide missions in order to keep them out of his hair. You can imagine how frustrating this must have been to Kael, who was dealing with the fact that 90% of his populace had just been, you know, genocided. Every last soldier he had was important. The Alliance sending him on suicide missions wasn’t going to fly with him.
So when the Naga showed up and offered their aid, Kael reluctantly accepted.
The humans found out about this cooperation and weren’t particularly pleased, so Kael and the other blood elves were locked away in the dungeons of Dalaran. That is, until Lady Vashj came, once again, to the rescue. She was the one who explained to Kael exactly what the odd cravings his people were having for magic were, and she also told him that she knew a guy who could help.
That guy who could help? His name was Illidan. Now you readers have probably got the warning bells going off in your head, but remember what Kael’s state of mind was: Silvermoon was in ruins, remnant Scourge and the Amani trolls were taking advantage of this fact, and the Alliance was actively making things worse by throwing the few remaining blood elf lives away. What else was he gonna do?
So off he went to Outland to find Illidan. And that’s about when it all started to go south for poor Kael and company and he began his slow descent into madness. But you can’t blame the guy for trying. And hey, you gotta respect someone who can kill a level 100 with falling damage.