You have to differentiate between Hijab, which means covering the hair, and Niqab, which means covering the face. The vast majority of Islamic religious scholars agree that the first is a must, while the second is only a choice. What you have mentioned is one of many misuses of Niqab, I heard many stories about people using it in committing crimes, and even terrorist attacks. I understand the security threat caused by Niqab, but I totally don't get it when people start to attack hijab...again it is just a piece of cloth wore on the head...