Celtic Soul - in answer to your question of last paragraph: If it were a regular occurance I'd be miffed, but if it were just an occasional thing then I'd not be too concerned.
I don't think it's realistic to expect a festival campsite to be quiet at night (irrespective of the rights and wrongs).
I used to hate the noise on campsites at night & would lie awake, desperately trying to get to sleep. Once I learnt the trick of not worrying about getting to sleep I found that even if I didn't actually sleep much, just lying inactive & peacefully listening would be almost as refreshing as having slept.
I do sympathise with people who want peace & quiet - but I'm afraid that isn't enough to stop me singing thru the night. The spirit of the moment calls very loudly I'm afraid.

Kris