In my opinion, if you start taking kids out of school for the sake of a holiday, and your kids fail key exams or fall behind, its your fault and yours alone. But parents will blame schools.
It will also result in parents demanding to know the curriculum so they can best plan to take the family away. Teachers have enough crap to deal with, without having to answer to parents that want to dictate to the school. You are already getting a free education, don't take the piss.
All that will happen if it keeps happening is that holiday companies will put up prices at other times as well. And what about those people without kids, that enjoy going on holiday and not having kids running around everywhere?
You have to make choices in life. If you want kids, you have to accept everything that comes with that. If you want cheap holidays, don't have kids. You can't have everything in life.
Personally I believe a full education is more important than a cheap holiday. It might only be a week or a few days, but could potentially have quite significant impact later on. Unlikely, but it could happen.