I know you mean well but this is an inaccurate generalization. I have taught at a voucher school myself and know many families who participate in the program.
One of my good friends is the single mother of four (three at home)- she works full time, always has, drives used cars and owns her home. Her income falls within the limits necessary to get a voucher, so her kids go to private schools on vouchers. Her income has also been low enough for her to get food stamps and Medicaid insurance at various times. Her kids aren't perfect (what kid is?) but they're hardly headed for gangstaville either and she feels these private schools have done better by them than the local publik skools.
I could go on and on. I enjoyed part of my day yesterday with a couple that has actively fought for vouchers. Their kids and grandchildren are in both private and public schools. Again, not a junior gangsta or gangstarette in the bunch- one of their grandsons leaves to start college next month. He went to some private and some public schools.
I could go on and on but you get the point- vouchers allow decent, hardworking but still low-income parents to do better by their child's education. Until we can do better, I will support vouchers.