From what I've read, voucher schools don't outperform public schools, despite having advantages such as freedom to attract the best teachers, and being able to kick kids out for disabilities, behavioral issues, and low test scores.
In addition, I'm of the opinion that a voucher school system still needs to be backed up by public schools, for a number of reasons:
1. To make up for capacity shortages. There's no evidence that voucher schools would voluntarily maintain a surplus of seats, and there could be entire regions with permanent under-capacity, leaving kids with no schools to attend.
2. To bail out voucher schools that fail. At the very least I'd like to be assured (via legislation) that no public money will be spent to pay the debts of charter schools that are taken over by the state or by municipalities.
3. To educate kids who can't get into a voucher school.
Expecting healthy competition, after experiencing passenger aviation, cable TV service, or consumer banking, seems like a pipe dream.
An additional concern, which I don't know how to analyze: The number of passenger miles per day spent transporting kids to far-flung schools.