Public education for our society's children is not something that only impacts parents who have children or those children themselves. Educating our next generation is something that should matter to every person in society, and therefore it makes sense that general tax dollars should go to help make the system better.
The public education system, like with most government programs, is wasteful and inefficient at doing what its suppose to do. Public schools are in every sense of the word a monopoly. Regardless of whether you have kids or if you choose to opt with the alternatives, you are forced to contribute. Public schools will never get better, regardless of how much money is thrown at them. They have in fact already tried this in Kansas City. If you want underperforming kids to do better in school, get their parents invested. How do you get their parents invested? Make them financially invested. The more private schools you have, the cheaper the tuition will be, provided there are no government subsidies.
Even you are not using the public school system or typically avoid it when it comes to finding a place for your children to get an education at it does not mean they should not help the public schools get better. Our taxes should go to public schools whether we use them or not.