Matthew Yglesias responds that doxa is not episteme:
The voucher pilot program in DC, much like other voucher programs in inner-city areas, is good at doing what markets do best -- delivering consumer satisfaction. As Hiatt's column points out, parents with kids in the program are generally much happier than parents with kids not in the program, and there are many more applicants for "Opportunity Scholarships" than there are scholarships to hand out.
One thing missing from Hiatt's long, entirely laudatory, article about DC vouchers, however, is any evidence that educational outcomes are improving as a result.
Yglesias doesn't want to offend the teachers unions until the social science forces him to. (I respect him enough to think he would then.) But this leaves him open to some objections:
1. The social science can't even exist unless vouchers are allowed. We already know that private schools do better than public schools, even when socio-economic variables are taken into account. The difficulty is that children of parents able and willing to spend a large amount of money to educate their children are not like other children. But data about the success of market schools where participation is paid for requires market schools where participation is paid for.
2. As a moral matter, parental belief about whether the school is good ought to count for something, whether or not some quantitative measure backs up that belief. After all, parents are the ones responsible for their children's well being, absent serious abuse. They may make mistakes, but they will care more than social scientists and teachers' unions. Plato's view that children should be taken away from parents and given to experts to rear doesn't have a lot of explicit support in our culture, although it does seem to be the basis of the public school monopoly.