The problem is parents have no other options, and they have been trying to fix it for years, decades even, but they keep making it worse.
Vouchers is a solution that has proven successes in states that do them.
The arguement for funding planned parenthood is that abortion is only 10% (or whatever the small figure is) of what they do, and that we supposedly don't pay for that part.
Religious schools provide educational services that aren't religious in nature. All that we have to say is that vouchers can't pay for religious studies. There's no reason a student cant take math, reading, history, science, etc. At these schools. There could even be creationism vs. Evolution clauses in voucher rules that render schools ineligible for vouchers.