> What's to prepare them for that when they're homeschooled?
Life. The homeschoolers I know do tons of things that help them explore life. There are too many to list here, but here's a short list of excellent things homeschoolers do that incidentally help them learn about life: dancing (contra, waltz, swing, etc.); running your own lawn care company; babysitting special needs children; babysitting in general; mission trips to foreign countries; film-making (for fun, commercials, competitions, etc.); learning to fly airplanes; regional equivalents of boy scouts (4H, boy scouts, something else that I can't remember the name of); and much more.
Edit: added word "frequently"
I definitely do not think being bullied is a good way to learn about life.
There's a good chance your kid is one of the 80% of children that isn't picked on. Even better: your kid might be one of the bullies, then you get the chance to really set things right.
Also, high school might be much worse, fragile children trying to become something resembling adulthood, preparing for life decisions. What's to prepare them for that when they're homeschooled?