[jaymmartin]

They stated why. If you allow people with the means to do so to opt-out of a system, they do not participate in the system. The system now loses the governance and to some degree resources of those people with means.

More specifically, rich families put their kids through private schools and abandon the public school system. Without skin in the game, they vote to reduce the budget of the public school system. Rich families generally have more time and resources to spend being involved in the schools. They won't be spending those resources advocating for improving the public school systems. Additionally, their kids, who are well-cared for and come from a family who values education, do not form a peer group with the other less fortunate kids. This deprives those kids of better peers to model.

Now, you can argue that the freedom of and benefits to the rich families trumps the benefits that the poorer families would receive, but there is a greater good argument.

I've seen it argued that universal social programs are generally seen to work better and are more popular compared to means-tested ones. For example, Medicare and social security vs Medicaid and TANF.