no he has reason:the fact that he is that old typical sort of villain,with no reasons to be one as if he was born evil.that's what some people love and i hate about him.
the villains of naruto are the only villains which seem to fall in the category of reality,with good reasons to do so,other manga just copy the dbz shit of pure evil theory.i mean like it or not,even the greatest terrorist wouldn't have had just wake up and said,"alright,today i am blow america's world trade centre up,muhhahhaa...
the only factor that doesn't work in the real word which is shown in naruto is the tnj factor to that extent,other things are totally valid.
he wants 2 bcum greatest entity in soul society.

as 4 as OT his looks:yayy: