Why can the blood elves kill Prince Kael'thas?

This has really been changed by BLZ. Originally, Kael'thas led the blood elves, but Kael'thas took refuge in Illidan, the Burning Legion. The Burning Legion is the public enemy of all Azeroth, and the blood elves have a deep hatred with natural disasters (natural disasters also belong to the Burning Legion). This almost led to the genocide of the blood elves, so the blood elves overthrew their prince and king Kael'thas and chose a new regent. Because he and the dark night are enemies of the world, and the enemies of the enemy are friends, he took refuge in the tribe. The Dark Queen was once the Lord of the Blood Elves Rangers, so the tribe accepted the Blood Elves easily.

Kael'thas occupied the storm fortress and forged a deep hatred with Nalu, while another blood elf force-Oracle-left Kael'thas and took refuge in Nalu. The actual situation is obvious. A blood elf has been divided into three factions, one is still attached to Kael'thas, the other is secretly trying to transform the blood elf with a new model, and the other is openly confronting Kael'thas. In such a complicated situation, the blood elves still have reasons not to kill Kael'thas, which is obviously insufficient.