This is a valid concern but reveals the assumption that institutions are better at raising kids than their parents are. Unfortunately there are many instances when a good teacher is a better influence on a kid than their parents. But to conclude from this that school choice would worsen education is a lie. Parent know how to pick better products and services, even if they are bad parents. They can pick iPhone over android. They can go see a good movie instead of a bad one. They want their children to learn as to have strong moral character, even I'd they are too inept to do it themselves.
More importantly, there are enough involved and caring parents which will weed out the bad teachers and bad schools, and raising up the good ones. The bad parents will benefit from the involved parents and will actually empower bad parents to become more involved with their kids education. Ask any teacher - a loving and involved family is the biggest determinant in school success.
By disempowering parents we are not doing them any favors. Its the whole elitest Nanny state philosophy.
Not better at raising children, but educating them? Yeah, I do believe that, generally speaking, someone who receives at least four years of specialized training in a subject is better qualified to analyze that field than an average consumer. Though I know my driving habits better than the engineers at Ford, Honda or Chevy, I trust them to be better at figuring out how to make a safe, reliable car than I would be.
(And no, I don't blindly believe all teachers are good teachers, so don't pigeonhole me as a teacher union apologist. And yes, I recognize that there are exceptions to all general statements.)
I know of an ongoing situation where a parent has gone through four advocates trying to get someone to affirm her belief that her child is a "special ed" child with an emotional disorder. All of the impartial advocates have told the mother that the child doesn't meet the criteria, yet the mother keeps pushing the issue. It's nearly Munchhausens-esque.
Our culture has reached a point where if a child can't in some way be labeled "exceptional" or "special" even as being specially challenged parents don't know what to do. If you raise an "average" kid these days who doesn't need some sort of support but who isn't brilliant, the parents almost feel like a failure. These days, it seems like a parent would rather have a medical excuse why a child isn't brilliant than be content with an ordinary, average child.