Which is why the support for this has sorta died out. Most religious schools have administrators that recognize that with public money comes government control (which is not necessarily bad). But, if your institution primarily exists because you don't want the government removing your religious beliefs from education, you've got a problem.

Hence the public schools don't want a voucher system, since they'll lose funding. Most religious private schools don't want a voucher system, since they'll lose control. So pretty much all you have left is the non-religious or marginally religious schools that still want it, and that's a huge minority.