I think you are just misunderstanding what sort of anti-religious stance people have on AB. I'm sure I speak for the majority here, when I say that we are usually anti-religion and anti the concept, but very much not anti those who are religious themselves (so long as such people practise their religion in relative privacy and don't use it as an excuse for violence or subjugation).
So burning a Koran, or a Bible, or tearing it apart, or chanting racist abuse, is just not acceptable and you don't need to be pro- or anti- anything to see this. The behaviour of these girls was grossly offensive and deserves to be seen as such in a court of law.
If they had done the same thing to Christians, then it would also be condemned as loudly. At the moment, for various reasons, it is Muslims who are the targets of such abuse. Not that many people these days are bothered enough about Christianity, in this country at least, to use it either as an excuse for violence or as a target of such actions.