I can conceive of a submissive personality who loves to hurt people but can only do so if ordered to do so... unable to bring themselves to decide what to inflict, how to inflict, or how hard to inflict... but gets hot and bothered when ordered to do so...

And it is very clear that a dominant does not have to be a sadist at all. Bondage enthusiasts are a great example... full control, but never causing pain.