So the typical objection to vouchers is that they would undermine the public school system and "leave behind" the weakest of of students. But that's always seemed to me largely nonsensical, given that the choice is between largely what we have now and a voucherized system - and that know we already have school choice. It's just one organized by geography and income.
It seems to me that the *real* objection to school choice - and this is where liberals' willingness to have other systems voucherized comes into play - is that it would trim the state's ability to use education to shape its future citizens. When people talk all swimmingly about "public education" and its "role in building our country" what they're channeling (perhaps only unconsciously) is the idea that education is about (in part) separating children from their parents' benighted, un-progressive views and turning them into constructive citizens. Voucherized systems would make that more difficult, I think. It's one of the reasons, after all, that the first "homeschoolers" really showed up among the hippies in the 1960s - they didn't want "the man" getting a hold of their kids.