Boy, HN loves articles about solitude and loneliness. And it's a distinction that often crops up in discussion here. I think there's a balance here, and cultivating some amount of loneliness -- not solitude -- is also good. For example, two people in my life are "Alice" and "Bob", who have been married for decades. Alice once told me that one of Bob's great weaknesses was that he'd been alone for too long in his teen…
Humans are tremendously varied, and in any group that is comfortable with solitude you will probably end up with representatives from many different sources of motivation for that. For everyone, though, I think there is definite benefit in either seeking to know one's self better or in seeking to understand the outlook other people have. By default we pretty much assume that everyone is mostly like us and this shortsightedness can lead to some pretty nasty evaluations of others who act in ways incongruous with the evaluators own worldview.
The article mentions that we invest a great deal in teaching children how to be social, but fail to prepare them for being alone. I would argue that we don't do a very good job with teaching kids to be social either, but we do certainly invest a great deal more on that side of things. It's one of those sorts of things that would be very difficult to change. If the parent or other teacher is not comfortable with solitude themselves, the only way to equip a child with a better capacity for it would require the teacher to actively teach things that they personally do not feel to be true. Very many parents, it seems to me anyway, are not emotionally mature enough to tackle this. A child which is comfortable with and who seeks solitude is literally worrisome for most parents today. That's the "loner", the "quiet one" that all of the lists of 'warning signs' for everything from suicide to school shootings are topped with.