darling, all the muslims in the uk that i know that wear niqaab, convert or not, did so against the wishes of their families and communities. in south asian cultures, which make up the most muslims in the uk, it is not a normal thing to do.
i do not wear niqaab. i do not see the necessity.
i think that if the school girl felt that strongly and she wasnt allowed to wear it at school, she should have considered alternative schooling such as home ed, there are large muslim home ed networks.
there are different intepretations of Quran and hadith.
long way i would accept your last point to be true. some muslim men do make unfounded and ignorant assumptions about those who do not cover, and stupidly can think that the commandment to lower their gaze doesnt apply.
lets consider secularization as a response to modernization. initially, due to secularization religious observance declined, but then due to consumerism and market choice which also applied to the realm of spiritual beliefs, religious or spiritual adherence stopped declining but took on different forms, so we observe a rise in paganism, wicca, celtic or new age religions, which followers would say are a continuation of an ancient, or older belief system, we see a rise in pentecostal and evangelical christianity, and we see an islamic revival.
this islamic revival could be seen as similar to celtic, aspirational indianism, or paganism as these women choose to adhere to a historical spiritual tradition of their region?
as for the invisibility of women once they enter the public sphere, i agree this has been the case, but i dont think it has to be. many of the women i know who wear niqaab are very active in the public sphere, and many muslim men, mostly the younger ones dont think of sisters who wear niqaab as invisible, as they still have a voice and are not afraid of using it. the older generation traditionally dont listen to anything the younger generation have to say, if it be about niqaab, or if their daughter/son wants to marry a different ethnicity etc and uses islam to demonstrate the permissibility of this, they still think they know better.