We were homeschoolers by last resort, too. I just had to get my child out of the school he was in, and I didn't want to put him into another school. Like your child, he was so far ahead, I figured that even if all we did was read books, go to the park, swim, bake cookies, and watch movies, then he would be better off then in that school.
And yes, children need to learn how to 'function in society,' but as adult we get to make decisions that kids aren't always afforded in schools. I didn't think that self-loathing and being bullied was the part of society a 7 year-old needs to learn about.
So know that if your child ever becomes extremely unhappy or depressed, please take it seriously. As adults we get to make decisions about how others treat us and set limits. Kids can't always do this.

This year my son is back to school, and he loves school. He has a lot of freedom to read what he likes, and is learning public speaking and other stuff. He is back to his happy self.