KKK much more scary, I agree, because the sole reason for wearing the outfit is hatred, and known to be.
Being unable to see the hair doesn't in itself interfere with recognition or interpretation (apart from making it more difficult to see the scalp going back, of course), so I have no problem with the hijab or the nun's coif and wimple.
Before yelnats mentioned nuns, I had wondered whether some covered their faces, but couldn't remember ever seeing this and probably never have in the flesh. If I'd googled "nuns eyes only" I'd have found the images for strict orders - most like a niqab in effect. And some Victorian widows wore heavy black veils, obscuring the eyes as well - so more like the burka!
If all but the eyes is hidden, does the niqab-wearer develop more fully other ways of adding nuance to speech or showing what they feel (with no speech) and would I adjust and tune in to these. Possibly, with time.
I've never spoken with someone wearing the full burka, so I have no idea about that. The resemblance to a black Dalek is unfortunate but I hope unintentional on the part of the Dalek designer.