I heard on a particular good program on Mohammed (by BBC) several Muslim women speak on why they did not wear a hijab nor cover themselves as the Arab cultures of ancient times did. One of these Muslim woman specifically stated, "The Koran tells us to cover our nakedness--not cover ourselves in black bags."
I then did a search on the topic and discovered this very quote from the Koran:
And tell the believing women to lower their gaze and guard their private parts from sin and not show of their adornment except only that which is apparent, and draw their headcovers over their necks and bosoms and not reveal their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, or their brothers' sons, or their sisters' sons, or their women (i.e., their sisters in Islam), or their female slaves whom their right hands possess, or old male servants free of physical desires, or small children who have no sense of women's nakedness. And let them not stamp their feet so as to reveal what they hide of their adornment. And turn unto Allah altogether, O you Believers, in order that you may attain success. [An-Nur, 24:31]
From this Koranic text it is clear that only outside the Koran come particular traditions for the hijab and other head or body coverings.
Knowing this information may enable you to discuss this topic more civilly.