It'd also take conscious effort to trigger the Swiftcast and then cast Sleep, and outside of gameplay (e.g. for story purposes) you probably couldn't do both quick enough to avoid getting arrested. The Brass Blades / Crystal Braves had no trouble roughing you up, as evidenced by Ilberd pretty much throwing you on the floor.

... and for the millionth time, we did not have a weapon and the game cannot assume you're a Black Mage or any other class.