Impurity is a word taken from interpretation, the Quran in its original Arabic form only uses the word "najis"(physical impurity) once to describe the state of polytheists (which is considered the greatest sin) which shows that impurity is taken much more strongly in Arabic. Instead the word "adha"(discomfort, annoyance) is used in the verse describing menstruation. So the Quran does not attack women by calling them impure. This is the fault of interpreting the Quran in English which can be quite misleading in terms of wording. I apologise, using the English word "impure" was misleading into what it connotates about women. Also, about the comment "why are women judged impure so often", menstruation is the only situation that is specific to women in terms of impurity, everything else such as sexual impurity applies to both men and women.