Many people have noted that the public school model is obviously unattractive when applied to other goods and services. For instance, few would support a shift to residentially-assigned, government-run grocery stores. It's much better to have a choice of grocery stores and to address issues of access with income supplementation.
But here’s another way of getting at the same idea. Think of attending school as a kind of occupation. Suppose that your place of work was dictated by the government based on where your house was located. Your boss might do a bad job. You might have serious conflicts with your co-workers. Your day-to-day work might be tedious and unproductive. But if that's the place of employment assigned to you based on your location, that's where you'll work.
Now suppose there's a much better workplace down the street. You'd prefer to work there. You're permitted to switch jobs, but there's a catch--your former employer will garnish your wages forever even though you no longer work there. You can't afford this lose of income, so you decide to stay.
I assume few would support a shift to this system of employment. Yet this is all too similar to our current system of public schooling.