I wish people would stop using random trash mobs in Icecrown and Sir Zeliek as a precedent for undead paladins. God forbid, a raid boss might be special lore wise...
Do you want to know the KEY differnce between all other types of paladins and the undead. The Light Magic they use doesn't hurt them to use.
Paladins use the stuff in truck lots. Hell, they even build it up now to fire our powerful Holy Light spells. So, unless you can make a possible excuse (lore-wise) for why a Forsaken wants to feel like he is getting set on fire everytime he got into combat. Your argument is basically "NO I'm right! We have Sir Zeliek and random nameless dead trash is Icecrown. They show us that they can happen lore-wise!"