[Well, Castiel canonically frightens the king of Hell into fleeing by showing him his true form, so your mileage may vary on that -- also as long as you don't have an angel blade, good luck trying.]
You aren't possessing a human, nor are you an immediate threat to anyone here. [He's here, that makes you a non-threat. Just give him an excuse to smite you on the spot.]
Those are the only reasons you still stand. [Yeah, the fear? Might be healthy right now.]