It's funny how after all these years that dreaded s word can still come up. It in the beginning it use to throw me through a loop and I used to get annoyed and didn't know how to answer. Now I just point out how school is not for socialization. Socializing at school means being sent to the principal office or letters home. Think about it! The only time a child can truly freely talk to the other children is at recess and maybe at lunch time. Although, some schools discourage talking at lunch time.
Homeschooling doesn't mean you are home all the time. There are still many of the same outlets available to homeschoolers. My kids still go to church, youth groups, scouts and chorus. Over the years they have, also, participated in sports. All of these things are after school programs. Programs that generally open themselves up to more socializing and free time with other children. Yes there are times within these programs where the kids have to listen this is especially true with sports and chorus, but relative to the time spent at these events and school there is more time for free talk or play. Plus there are homeschool groups that offer classes, field trips, holiday parties, and just time to hang out. My kids have friends they invite over or call on the phone regularly.
Really where a child goes to school (or not go) does not prevent them form socializing. Socializing takes place in the real world around all kinds of people and situations: grocery store, other stores, scouts, sports, church, post office, doctor office, nursing homes, soup kitchens, libraries, homeschool groups, etc.