We actually encountered quite a bit of hostility and criticism (how can you sacrifice your children for your principles, and the like). My husband went to Grammar school and did very well. I was educated in a country where there were NO private schools, apart from those for the ex-pats in Geneva and Zurich. Many in my OH's family went to top public schools.
We truly felt that sending our kids to private schools would NOT be beneficial to them. But, yes, we did make sure we lived in parts of town where they would go to 'good' schools, whatever that means (and what is 'good' for me maybe 'not so good or bad' for someone else). We sincerely believed that it is best for children to have to cope with all sorts of children, and to some extent to learn to cope with bullies - as bullies do exist in the adult world too. We also believed that 'prep' does not encourage children to take their own responsibility with homework, timing, etc. Because in adult life, there isn't always going to be somebody 'sitting on you' until you've done your work - so the sooner responsibility, initiative, timing, organisation, etc, is learnt - the better prepared to be autonomous and lead.
And we also believed sincerely that dividing society with private education is in the long run a recipe for disaster for society - where it is them against us, both ways. Where people do not understand how and why people are different, because they know and have regular contact with each other. The UK is a very divided society - with people from a very young age having little on no contact with sections of the population, and pointing the finger, or worse, at each other. So yes, you can protect your children from the outside, smaller classes, better grades, etc - but in the long run, I personally believe it is not good for the children and certainly not good for society - and dangerous for all.
When our daughters went to UNI, they couldn't believe how badly organised the ex private school students were. They could never hand an essay in time, and their behaviour re drink, sex, drugs, etc- was totally off the rails as they went berserk with all the sudden freedom.
The history of private education in the UK goes such a long way, but it is divisive imho, and is one of the important factors in our extremely divided society.