Not all users of the state system have the high moral ground.
I have neighbours whose children all go to grammar schools. They have been prepped for these since the age of 3 - private schools throughout which specialize in getting children into the local state grammars, including going into school during the holidays to practise exam papers etc.
The family could easily afford private schools, and in fact they had back-up places ready at good local independents. But they preferred to play the system. Therefore they stopped other children - who may have had less resources/less pushy parents - accessing this kind of education. I am sure this is by no means an unusual situation.
Using the private sector throughout the children's education, rather than just buying privilege to jump ahead of other 11 year olds, would actually be more decent. But perhaps these people can be dismissed because they have paid for (part of) their children's education?
What then, of our friends, who moved to a far more expensive house, so their children would be in the catchment area of the local outstanding primary school, and have had their oldest child tutored for the last three years (two more to go) with a view to getting her into the local grammar? They have paid for it just as much as the other family.
Many people, including many of the posters on this thread, use whatever advantages they can find to get their children the best education they can. If anyone has actually sacrificed their child's education by actively choosing to send them to a school which they know doesn't suit them best, specifically to support state education, for the good of the community or for future education reform in the country, that would be an interesting viewpoint. Otherwise everyone is probably pretty much in the same boat, and perhaps there should be a lot more acceptance of other people's decisions.