I've been meaning to comment on this thread for ages, not least because I was also at the festival and would have loved to have taken a photo too.
I completely agree with what you are doing, and not just because I want the photo. Once people start making up laws, and we accede to that, it's the end of a fair legal system.
One thing I do want to add though is not legal but sociological, but I think it's a big part of what is going on here. People are starting to believe that photos of children are in some way dangerous in themselves. So we should not be able to take photos in swimming pools, and photos of fully clothed children on the street in some unspoken way will inevitably lead to paedophilia. Of course these ideas sound insane when you write them down. but they are what underlies some of the less considered reactions.
What really brought this home to me was when I was in the park with my DD and her friend and her friend's mother. It was the school holidays, and there was a clump of teenagers hanging around in the infants playground on the equipment so that the two girls were a bit scared of using it. We asked them to move, and most of them did, but one girl refused and my friend had a bit of an argument with her. So my friend - who is much more confrontational that I would be - went away and rang the police, and then took a photo of the girl and her friends.
At which point the girl went ballistic, and rang her dad. She also got her friends to come over, and say, you took a photo of my friend, you must delete it. She did (although why she should have I am not entirely sure). Her dad then turned up, furious that we had taken a photo of his daughter. (My friend explained what had happened, said she had deleted the photo and daughter then got an earful for being a lout.)
And I was left standing there, going wtf? Do we really now believe that taking a photo of someone is stealing their soul? Or what? I am still boggled when I think about it.