Turn undead; how does it work?
If good and evil are objective variable cosmic forces then it follows that spells can be good and evil and that the results may contaminated by this. By this formula undead might be 7 parts negative, two parts positive to one part evil (evil because they contain the cosmic residue of the evil used in their creation and not because they are broadly negative beings).
The basic concept is that good and evil repel each other and attract like. It follows that any creature with "evil" as an essential part of its make up and life processes will be repelled by a strong source of "good".
In this model it also follows that if an undead creature was created without the use of evil then turn undead will do precisely jack.
"Undeath TM may contain evil"