Smith said:... Rakasha is propably blind... he is wearing mask without any hole for his eyes
Remember also that in some movies assassins like "ninjas" mask themselves sometimes to hide their faces. Still, Rakhassas other than hiding his identity, by completely hiding his face makes also harder to perceive his intentions in melee combat due to hiding the expressions of his face(and the look-glance of his eyes).
Another group that reminds me these stuff are some Harlequin assassins, but I don't remember where I have been remembering them from. ::)