And I just wonder… where?
Sure, people can point to acts from individual Blood Elves, among who even the victims of recognized that the “blood elven” perpetrator would never really be counted as one of them - because said perpetrator’s philosophy differed so much from the philosophy of the Blood Elves.
Which is mindboggling on two fronts. A High Elf recognized the extremely good in Blood Elves, but at the same time she hates them with a burning passion that could rival the sun. It is so extremely weird.
Which is also weird, because when the High Elves first taught the humans magic, the High Elves were the ones who had to step in to stop another legion spread at the hands of the humans. But that was in the Kirin’tor, so
They didn’t.
No one knew. The last thing the Night Elves knew was that Kael’thas helped them against Illidan.
Remember, the only ones who knew of Kael’thas joining up with Illidan was Maiev, and Maiev was imprisoned, her entire squad was killed. She never had any chance of reporting back.
Depending on what happened to the Ironforge dwarves who were with Garithos at the time of Sylvanas’ backstabbing, I would presume they died along with the rest of Garithos’ regiment, no one but the Blood Elves knew of Kael’thas’ dealings with Illidan, hell, if even anyone but Rommath and other magisters who were with Kael’thas initially knew, earlier Blood Elf lore (Before blizzard changed the race lore pages) stated that Rommath never really fully disclosed and told about Kael’thas’ dealings with Illidan and fel (The felfire crystals) because he feared it would create panic.
There was also another source, that gives us a canonical timeline on when things happened. So allegedly, the Blood Elves joining up with the Horde happened before the Draenei crashed on Azeroth.
All in all, something very weird happened, but no one, until we reached Shattrath, knew about Kael’thas’ dealings with Illidan and then the Legion, and at that time the Blood Elves of Silvermoon also swore that they would personally take responsible for their fallen prince, so they made it very clear that they were not with Kael’thas at that point.