One of the great sacrifices of subjecting kids to school is that it trains them to ask for permission for everything, from turning in work late, to changing to a different class, to more mundane things like going to the bathroom. It's a tradeoff, of course: condition kids to seek permission for everything, and by doing so enable a system to exist where they receive an education.
Maybe that's a worthwhile tradeoff, and maybe it's not. But the real harm in it, in my opinion anyway, is that when we leave school, we're still in the habit of asking permission for everything. That's dangerous.
A manifestation of this that I come across with frequently is the questions that people send me by email. Here's a paraphrased template, which covers a good 60%+ of the emails I get from strangers:
I've been saying that college is obsolete for a very long time. I dropped out in 2000, because even back then I could see that it was a really poor value proposition. I didn't predict this because I'm some crazy genius, but because I'm willing to discard emotional attachment and stare plainly at the facts.
School is outrageously expensive, leaving graduates with a debt (or net expenditure) of tens of thousands of dollars-- sometimes even one or two hundred thousand. There are some things that are worth that amount of money, but for many people school isn't one of them. In fact, apart from very specific cases, I think that school is a bad thing, not worth doing even if it was free.
That's not to say that school has no benefits whatsoever. It does, and although I left with zero additional skills after my three semesters there, I had a good time and benefited from the social aspect. The problem is that you can't just compare college to doing nothing at all. You have to compare it to what you COULD have done.