HOA....yes, I agree, the majority care. And I have no problem at all with people finding the best they can for their child, especially if SEN are involved and not catered for elsewhere.
But....if I do end up sending my dds to indie secondaries (unlikely, but possible if the current improvements of the local state school go pear-shaped to the point of misery/danger), I shall still try and support our local comp. I'm nothing to do with education per se, but have become a parent Gov at the primary school, could offer similar involvement at secondary, or be one of the many parents who mentor older children there, or fundraise for something that would make a difference.
It does take a lot of parents to make a difference, admittedly. Locally, because of need, its happening - the critical mass has been reached, and involved, pro-active parents have started to defy years of habit and are sending their children to the local comp. With almost instantaneous effects. It just took a brave few to start the ball rolling. They got involved on all levels, and took advantage of a new academy status.
I repeat....women got the vote. Black Americans got the vote. Things change when enough people want them to, and a group get together and don't give up.