Thats the character though.
All the classes and jobs so far, besides BLM, have essential been about goodie two shoes teaching us how to goodie two shoe our way through their job. Dark Knight would have been an excellent opportunity to add a job that was portrayed a bit more evilly, or at least a bit less good.
Just because we're always good, doesn't mean everything we touch has to be golden.
Afterthought: The Paladin quest actually features the most 'Evil' people of a player character job. Isn't that weird?