Originally Posted by
banestalker
Let's roll back to BC days. Blood Elves had no Sunwell, their source of power was gone and they needed a way to feed their addiction. some human jackass mistreated them and imprisoned Kael'Thas and his followers for their questionable methods. (and his own xenophobic mentality)
They group up with Nagas and escape Azeroth, make their way into Outland, meet illidan who tells Kael'thas there's a way to feed the addiction : Fel Magic.
so Blood Elves replace their arcane source of power with Fel source. you can see the green crystals scattered in their zones. they feed on demonic energies which made Alliance wary of them. to the Alliance the Blood Elves were a lost cause, and Blood Elves thought the Alliance abandoned them in their moment of need. Blood Elves knew Fel magic was dangerous but they had no choice, they wanted to control fel energy source not lose themselves to it and THAT made blood elves interesting.
but after their redemption story in BC they slowly returned to their noble past, now they're basically High Elves again. hell, they're even nobler because now they use light as an energy source and not arcane. imo lorewise there's nothing that explains their loyalty to Horde now, they're neighbors of Forsaken who have a hatred for everything that has a beating heart, their allies in Kalimdor are savage tribals.
I guess Blizzard didn't have a long-term plan when they threw Velen into the Sunwell to cure it with light energies.