How does one respond to those who interpret the noble verse "and to draw their headcovers over their bosoms" as not indicating the obligation of hijab, but rather as merely evidence of modesty?

The words of the Almighty: (And not expose their adornment except that which [necessarily] appears thereof; and to draw their headcovers over their bosoms. And not expose their adornment except to their husbands, their fathers, their husbands' fathers) [An-Nur 24:31] are evidence for the obligation of hijab, not for its removal. Some scholars have used this verse as evidence for the permissibility of uncovering the face and hands if there is no fitnah (temptation/strife), but they must be covered if fitnah is feared or certain.