I can't believe how quickly parents in this country have been brainwashed by this. The outrage at the OP is ridiculous.
This is particularly silly and confused:
"Can you believe that as an adult, you have to seek permission from an employer to take yourself abroad, or risk going anyway and being sacked?
Why is it different when you choose to send your child to a school?"
The difference is so blindingly obvious that I can't believe I am going to explain it, but I will.
When you take a job, you explicitly contract to do certain hours of work and you are essentially selling your time. Not to provide them with the hours or days of work you have promised is to renege on your contract; it is the fact that you are being paid for work that you have promised to do that makes it wrong. In other words, once you are on that salary you owe them the days' work in the same way you owe your mortgage payments to the bank. It is no longer your time to choose what to do with; you have sold it.
When you send a child to school, you are availing yourself of a service that the local authority provides to your children. You, as a parent, are responsible for providing your children with an education, and the local authority is responsible for making it available through schools. The transactional nature of owing time to a school simply does not exist. You have not sold your child's time to the school and you are receiving no payment in return for it. On the contrary, you have paid (via taxes) for schooling for your child and your availing yourself of it.
What you do owe - ethically - is a decent education to your child, in the same way that you owe them a decent upbringing in all respects. The detail of how you manage it should be up to your discretion as a parent. In a looser and more general way, you owe certain courtesies to society and the professionals educating your child, but it is a recent thing that this social contract has been tightened and distorted to this extent. Making criminals of parents who don't "obey" term times.... this is rather a sledgehammer to crack a nut.
This is a choice, made by a certain government, it is not a natural state of affairs. To be surprised by it and even resistant to it is not to be somehow hard of understanding. In fact the opposite is the case - to be so myopically convinced that things can't be any other way, is rather tragic and craven
Coming back to the misguided analogy with employment: if you didn't have enough leave to take but you were dying to take up an opportunity to go to a wedding abroad, or something like that, a reasonable boss would try to exercise common sense and sympathy and temporarily release you from your contract, i.e., offer you unpaid leave.