Oh, absolutely. Much better then fel energy did, which had its own problems. [He shuts his eyes just long enough to tap a lid with a finger. Guess what causes an evil glow!]

But Prince Kael'thas betrayed pretty much everyone, allying with the Burning Legion. When his own people refused to join in on his madness, his agents stole M'uru back, finalizing his corruption into a twisted shadow of the Light. At that, the Blood Knights realized they had walked a false path, and renounced their loyalties to Kael'thas.