It wouldn't be draining money, since public schools would get money per-student just like private schools do (conversely, why does the local public school get t

It wouldn't be draining money, since public schools would get money per-student just like private schools do (conversely, why does the local public school get to count private-school students in its catchment area?). And you're assuming that it's possible to make all public schools good, which from what I can tell is roughly impossible to do given American political realities.