The Libertarian Utopia is never to be. Many people, when left to their own devices, unfortunately do not make good decisions. They tend to take the low road, even with legal majority with all its intended attendant responsibilities. But many parents fail. Socially we take up this responsibility through our government.
Abandoned kids tend to become sociopaths and act out for attention.
If their parents do not care and society does not care, they are usually lost. And that has consequences for all of us. If you have never interacted with a child at risk, you might not inherently know the potential there that has been twisted and abused beyond comprehension. And if you have never seen one of these kids get his act together in a social program, where his parents failed him, you might not appreciate the power of society. What people do in public and what people do in private are two totally different things.