This is hard - I don't know what we would have done if our local schools had been 'bad' (whatever that means, my 'bad' could be your 'good'). And yet, what I have been trying to say is that it is a vicious circle. Same for the health service. Schools which have some problems, become worse and worse as those who can afford it, who are also often those who have more influence and clout, jump ship. If all the parents who could make a difference and influence things leave- then schools become more and more polarised.
It is very difficult in the UK, as things have gone so far for far too long- with a long traditions of (so-called) public schools and fee paying schools, CofE and other denominational schools, etc. In most other European countries, this has not been the case, and children have always grown up and been educated in mixed social groups- and the parents who can support the whole school for all the children. The concept of 'doing one's best for one's children' - even if to the detriment of others, and society at large, is an anathema- as it is detrimental to all in the long term.
I'd perhaps make a comparison with the immunisation of children - what is more important, the right of an individual to say 'no' - with the current huge increase in diseases like measles, etc- with the enormous risks involved. Or the rights of children as a whole being protected by a 90%+ immunisation. In many countries, children are not accepted into school until their immunisations are up-to-date- and this is accepted as best for all. My parents always taught me that my 'rights' had to be curtailed if it affected the rights of others.
I am fully aware this might be controversial, but the bigger picture is sometimes more important than the individual. Do we want a society which is so polarised that the 'lucky and better off' cannot play in the park or walk to school safely? Think of the situation in South Africa for instance- where anyone with a higher standard of living has to drive the children to school armed with a tazer and a gun - and live behind electrified fences. We do get the society we deserve sometimes.
Here all the kids go to the local school, and walk there happily together, rich or poor, irrespective of class, colour and religion. We always felt that it was our duty to help the school system for all, not just our own- and that in the end, it would also benefit our children in a different way.