I agree with most of what you are saying bloss, but it's impossible to be unspecific about reasons. Otherwise how would we be able to talk about it?
And though I agree with and applaud fennel's post, my choice would not be based solely on a long-term social goal. In the shorter term, I think it's important for a child to be part of a vibrant and diverse local community for the good of their self-esteem. quality of life, and sensitivity and understanding of the world and people in it.
A school is only a microcosm I know but to start narrowing down the people your children come into contact with at such an early stage sits uncomfortably with me. I know parents in my area who have chosen a different state school in the town because it has a higher ethnic mix and they wanted their children to be more aware of the multi-ethnicity of our society, and I support them in that decision.
and my other point is financial and it has to be. All other things can never be equal, because that's a massive amount of money to have to make a decision about. I don't see why private education is the be-all and end-all of choice for children. If I had the money I would put it towards something else; as I've said, towards a university education, or towards a house deposit, or all those other things that I found easier than my children will because of the changes in further education funding and the housing market we've seen over the last 10 years which I fear will make things impossible for the next generation.
Sending my kids to private school won't make it any easier for them to pay for their university place or buy a house, but having a little money left for those things would leave them able to choose a career based on what they wanted to do rather than what would pay for them to buy themselves out of a potential financial mess.
I do know from my marketing experience that when you give things for free, they are perceived to have less value, and I do wonder sometimes if there is a boost in the perception of quality when parents are paying for their child's education. But I have nothing to back that up.