For socialization, there's after school activities like 4H, scouting, etc. Plus hanging out with neighborhood kids.
My area has after-school sports organized under the township rather than the school, so any resident child can join the softball and soccer teams.
You also have homeschool groups, where the homeschool kids of an area can do field trips, do plays, etc.
When confronted with the question, “what about socialization?” I would respond with a list of extracurricular activities we were involved in and the comment, “if he were any more socialized, we wouldn’t have time to do school.”
My family are now second generation homeschoolers. Our daughter home schools her children and our son sends his to a classical Christian hybrid school, where as well as full day students, some attend only half days and homeschooled the rest of their subjects. That’s a great concept for students whose parents don’t feel confident enough to teach every subject.