>>719025812
Except getting Arthas to take Frostmourne and come shatter the ice containing his soul was how Ner'zhul turned against the Burning Legion. Mal'ganis even thinks tricking Arthas into going to Northrend to get corrupted by Frostmourne is all Part Of The Plan.

Ner'zhul was only a victim in that he did something stupid and was being punished for it.