Parents are made to feel it is morally unacceptable to pay for an education, says a private schools leader.
HMC chairman Tim Hands said there was an "illogicality" about families buying a house near a good school but not being willing to pay school fees.
Parents clearly felt it was more morally acceptable to buy an expensive car or holiday, the Headmasters' and Headmistresses' Conference heard.
Average fees in UK private schools are £14,000 a year.
For boarders it tops £27,600 a year - more than the average yearly wage in England.
Michael Pyke, a spokesman for the Campaign for State Education, said: "It's inevitable that parents will try to seek advantages for their own children and there is no point anybody arguing the reverse.
"If we want a fairer education system it has to be brought about by political means."
But Mr Hands said parents were making illogical choices and that private schools, such as those in his association, were wrongly attacked for restricting social mobility because of the fees they charged.
He stressed that 36% of pupils in HMC schools across the UK received help with their fees.
And he told heads at the group's annual meeting in London: "Tony Blair, opening a London Academy in 2005, talked of the different ways in which parents could transform their child's education.
"Examples included moving house in order to access a better school and employing a personal tutor - one quarter of all parents in London pay for private tuition in the course of their child's school career.
"Moral opprobrium attached to neither of these, though the latter is of course paying for a private education, and the former is not social but postcode mobility, potentially productive of social division."
He added: "Making the journey to independent education, parents are currently made to feel, is an unacceptable mobility - expenditure on purchase of a car, holiday or house is moral; expenditure on the education of the child is not. The illogicality is clear."
Speaking to reporters ahead of the conference, Mr Hands, said he felt that "over the decades parents have come to feel more bothered about the concept of private education and that has been politically encouraged".
He highlighted how both Tony Blair and Liberal Democrat leader Nick Clegg had sent their children to the London Oratory - a high-achieving Catholic state school in Brompton, south-west London with a reported 6% of pupils eligible for free school meals.
And he compared this with Christ's Hospital School, in West Sussex, where he said 88% of pupils were on means-tested bursaries and almost half of pupils paid 10% of full fees.