I look at evil as low level spirits who Know No Better..
Anyone who truley Has Contact with the Other side will tell you.
that Earth bound spirits are usually the trouble makers and are Really Just calling out for help..and are usually Just scared and lost.
some other earthbound spirits Have no Idea that they Have even Died.
It could be the result of an accident and they are in Shock and have attached them selves to somone elses aura..
Dont Get Me wrong all Evil spirits are Not Just earthbound spirits.
There Is Darker Spirits..But Im Not willing to go there...
Its deffenelty Not Just BLACK/WHITE....there Is alot of Grey areas..

This Is Not Gospel It is only my opinion...