What other part of life do you interact with only people who were born in the same year as you were (and, in the case of some schools, only your sex)?
Homeschooled children (in my experience) learn to make friends with kids a lot older and younger than they are. They also learn to look after and teach younger ones, and learn from older ones.
I went to public school myself, my wife was homeschooled (for all but two high school years), and we homeschool our five kids. There’s pretty much no reason I’d consider sending them to school, unless they want to in their high school years (so far our oldest doesn’t).