I’m no psychologist, but it dawned on me what Frostmourne really is or was. A mourne blade, aka soul container. That much I understood, but now I know how it actually works.
It cleaves beings into two sections. It absorbs the Ego and SuperEgo and leaves only the id. The “id” has no checks and the being is a mindless zombie left to raw instinct, aggression, deadly pleasures, infantile, impulsive and self preserving (such was the case with Sylvanas). For those who had great intelligence and powerful spirit (such as the elves) they became immortal death knights and warriors.
The weak willed humanoids reverted to the basest form of existence, pure monsters. The scourge, zombies, and tragic abominations.
Also, I found this little quote that seems to have be lost to the annuls of time.
"The runeblade is an extension of your being. A death knight cannot battle without a runeblade.” Instructor Razuvious
