By going in holdiday during the school holidays you are not being taken advantage of. In fact people who go at off-peak times are actually subsidising your holiday.
For your holiday to exist there needs to be some infastructure, some transport and some staff. These cost a lot of money and cannot easily be switched on and off. So by offering this capacity at a lower cost off season they are able to recover some of the costs of having the resources available at the profitable time when demand peaks.
If they weren't able to do this then even more of the overheads would need to be absorbed within the price of you peak week holiday. Thus you would be paying more.
Holiday companies are not charities or a public service, if they could sell low season holidays more do you not think they would?
Maybe we should go full comunist and set up some sort of public body to offer "free at the point of delivery" holidays. We could call it the National Holiday Service.