Once we are clear about the principles, the aims of education in a democratic society, then we can begin to reason out optimal ways of providing for their realization.
Elementary and secondary education became compulsory when our society decided that they had become the minimal educational requirement of a competent citizen. But there is a wide gap between minimal and optimal, and if the public recognizes a public interest in making something of some kind universally and freely available, then it is in the public’s interest to do so. What exactly we make available can be diverse and is always subject to discussion, but I think it’s clear that something more for those who elect it would probably pay dividends to the public good.
We started down several such roads many, many years ago. And then some forces pulled us back and down. I think it’s long past time to question whether those forces are really acting in our best interest.