Here are some ways that homeschoolers answer this question:
1) "Go to your local middle school, junior high, or high school, walk down the hallways, and tell me which behavior you see that you think our son should emulate." That's a quote from this article.
2) Ew, socialization is creepy. It reminds me of those residential schools they used to make Australian and Canadian natives attend to teach them how to be proper British subjects. Wait, do you mean "social outlets"? Homeschoolers have a lot more time for this type of thing than their school-schooled counterparts. See this article.
3) The socialization that occurs in schools is an unnatural kind of socialization. Children are divided according to age and they never get a chance to socialize with children of other ages or with adults. And this is the type of socialization that is supposed to prepare children for the "real world"? Homeschooled children meet all different types of people and choose their friends according to interest. This article explains things nicely.
This is a pretty funny compilation that one woman made of socialization questions that her readers have been asked. This one's my favorite: "She informed me that I really need to expose my kids to more germs on a regular basis so that they don't get sick 'when they are around people.'" That's funny.
This fake interview about homeschooling is also funny. I like this portion the best:
SB: So maybe school isn't such a great place for learning the positive aspects of socialization, but what about the other side? We all need to learn to be tough, to deal with bullies and smart alecks and people who don't like us.
DS: I'm sorry to keep answering you with questions, Sandy, but if one of your co-workers called you nasty names every day, or if they knocked your papers out of your hands and cornered you in the restroom and threatened you or stole your money, what would you do? This really is an important issue -- please tell me what you would really do.
SB: I'd probably sue the pants off them.
DS: Do you think a jury would be on your side?
SB: If they weren't, I'd say something was definitely wrong with people's thinking.
DS: Do you think people would understand if you said you had been so traumatized by your co-worker's treatment that you decided to seek therapy?
SB: I'm sure they would.
DS: Didn't you learn how to handle all that sort of thing in school without falling apart? Didn't school toughen you up for the real world, where co-workers harass you and pick on you, call you names, make your life miserable?SB: Point well-taken.
Another thing to think about is that, in recent years, schools have been cutting recess time to make more time for the children to learn what they need to know to pass the standardized tests. If the concern is about "socializing," then school-schooled kids are now worse off than homeschooled kids. School truly becomes a place for "socialization," that is, "the process of learning interpersonal and interactional skills that are in conformity with the values of one's society." When kids are taught in government schools how to "socialize," they are being "place[d] under government or group ownership or control." (Definitions here.)
Socialization, one of the main topics that people bring up as a reason not to homeschool, is actually one of the main reasons that people should homeschool.