OneWithTheForce, to be fair, as Turncoat says it does depend on where you live, how many other people are free in the day, whether you have transport etc.
I did reflect on it, but realised it would be a no-go for us because dd is the kind of person who wants to be part of a crowd, I don't drive, most of the people available for socialisation purposes were at school all day, HE'ding circles depended on car driving for meet-ups and most of my own social circle consists of people I work with, which is some distance from our home. Also most of the HE'ders I knew were people rather similar to myself in education and general outlook and dd needed more variety. No doubt she could have been socialised (as in taught social skills) by simply going to after-school activities but she would have felt very lonely in the day. Which wouldn't be a problem for a more introvert child, but a big problem for her.
For somebody else in a different situation, none of those things would be issues at all. Most HE'ders seem to do very well on that score. But it's all individual.
For my friend who pulled her ds out of school when she realised he wasn't interacting with anyone or learning a thing (ASD), HE meant a massive improvement both in terms of social activities (being free of the stress of school, he could cope with extra-curricular activities) and of learning. He is off to university in the autumn, having done very well both educationally and socially. Doesn't exactly look like a failure from where I'm standing...