For most kids you probably need some structure. For some, unschooling certainly works well; for others it's another term for "school dropout". I personally was both homeschooled and unschooled, for different topics, and a high % of the smartest people I know were unschooled.
I really struggled to learn to read and write, even by grade five. So my parents took me out and my mom worked with me one-on-one intensively to learn phonics, which finally fixed that problem. Meanwhile, prior to that the biggest challenge I had in learning programming on my own is that I struggled to actually read the books I had on it. I think that unschooling taught me how to learn on my own, in a way that was very beneficial later in life.
Yet again, I'd say based on my experience taking relatively high-level, proof-based, math classes in university many years later, that for me the structured experience of university math worked much better than trying to learn those subjects on my own (which I had also tried!). Yet, for high school math, there hadn't been much difference (I did attend highschool).
Learning isn't one-size-fits-all.
I was homeschooled but agree that it isn't for everyone, mainly because not everyone has the resources. It decidedly requires a middle class lifestyle. Also, parents need to have something of their life together beyond just financial resources.
But people overestimate the competence required of a parent to teach. Probably the biggest thing I learned was learning how to learn, and in particular, doing that on my own. So reading the textbook in college was hardly a shock. If my parents didn't understand a subject, they could learn it with me, or find the resources I needed (including community college, online courses).
Unschooling, however, I am not too sympathetic to. You need some structure.