This is always trotted out as a reason, but its idiotic. The class does not lose time because my child took a week off. All thats necessary is a word from teacher to parent "you might want to look at X as you missed it last week", if even that. It's not a problem anywhere but the UK, after all. Why do you struggle so with it?
And what about the children whose parent don't or can't catch them up on a variety of subjects (a lot of different subjects and material is covered in a whole week, let alone two). These students need to have the help in school.
It wont be just one child, many many parents take children out of school, it is cumulative effect.
Just because a point of view is different to yours doesn't make it "idiotic".
If people are so concerned about having a right to take their children out of school for a holiday, maybe they need to consider if state education is right for them, given one of the conditions is attendance.
The other options available to people have been pointed out on this thread several times.
If you wish to sue state education and take your child out for a holiday, you have to accept that you will receive a fine.