Opponents of school choice in its many forms often talk about processes and institutions and policies, but one way to grasp choice-created problems is simple, old fashioned, and non wonky. Just look at who is holding the purse strings.
In the public school system, the money is controlled by some combination of taxpayer-elected local school board members and taxpayer-elected state legislators (the nature of the combination varies by state). Every person who pays into the system gets a vote on how the system uses their money.
In a voucher or charter system, the money is controlled by the families of students. If you are a taxpayer without any children in the system, you have no say in how and where the money is spent.
If, for instance, you are a taxpayer in Indiana, you may watch in horror as Catholic schools bow to Archdiocese demands to fire gay teachers, and you may be further alarmed to know that your own tax dollars help fund those schools. But if you have no children, you get no vote. You will be taxed to support education in your state, but you will have no avenue for expressing your ideas about what form that spending should take.