Remember, the Light can be used to do evil just as death knight abilities can be used to do good.
Unless I have misunderstood WoW lore, the Scarlet Crusade is not precisely a āgoodā organization, even though they wield the Light.
The Light, I believe, answers to faith and self-righteousness. The wielder must believe in the Light, and they must believe that their cause is righteous.
I am definietely not very familiar with the ghoul term outside of WoW, but in WoW my impression is that they are just reanimated (and quite decomposed) corpses, without emotions or opinions. (They donāt seem to retain their soul, based on their behavior in WoW.)
As stated earlier, I concede that death knight abilities are nasty, but I still canāt consider the abilities evil.
As Lytherael exemplified, those nasty abilities can be used to save innocent lives; to serve the greater good, or to fight the greater ābadā - in which case I cannot consider them evil.
Furthermore, I have it on good authority that any āpresent dayā
(basically after the DK starting questline in WotLK)
death knight committing evil acts
would be slated for termination
by the Ebon Blade, the Horde, the Alliance, or all three factions.
āThe enemy of my enemy might be my friend, but I do not fraternize with evil.ā
I do agree that āunholyā DKs have less reason to feel good about themselves than āfrostā (and ābloodā might be somewhere between those two), but as I see it, itās all means to an end.
If I - a tormented, remorseful, self-loathing death knight,
who did atrocious things to innocent and good people when Arthas was my āpuppet masterā
- can use my dispicable, but powerful abilities to help the greater good;
to fight those who seek to destroy or enslave Azeroth and its inhabitantsā¦
I will. I will definitely not feel saintly about it, but I will feel better than if I did nothing.
Better than if I just lay down and let myself perish.
(Even though I might sometimes think to myself that I deserve to be terminated, for the horrible crimes I committed under Arthasā¦)