“Why is a woman in a long gown and a bonnet accepted — archaic, perhaps, but accepted? Why is a nun wearing a black gown and habit accepted? Why is a woman in a burka and hijab somehow threatening?”
You sound like a precocious teenager.
Gee, let’s see: because they sometimes kill people? Because women are usually forced to dress that way, because they’ve been turned into sex slaves by Muslim men, and mutilated by other Muslim women? Because that outfit is a symbol of Muslim supremacy?
“Hey, why is a guy wearing a white hood and robes somehow threatening?” See?