With peers as the parental substitute, immature decisions are inevitable. Pregnancy at a young age and outside of marriage, smoking, taking illegal drugs, etc. are all related to the strong influence of peers at the expense of parents. This may be socialization, but it is hardly of the type one wants for one's children. Compare such a narrow and negative social life to that of homeschoolers. Even if it is only the family, the child still has a more varied exposure to other ideas.
Time spent with adults, the parents, is far more than what schooled children get.
Add siblings to the picture and the view widens more. But more homeschoolers have far more. Most are in and about the world outside of the family. Groupings are not limited to children the same age. Classes are formed based on interest, not age, so the age spectrum is wide.