School is great. Not all of it obviously, and more for some people than others, but overall the pain and stresses of going to school were hugely outweighed by the fun and adventure of navigating through that system and interacting with all of those different peers and teachers. I wouldn't want to deny any kid those adventures and relationships and that exposure to our culture (for better and for worse). To be fair, I also grew up in a pretty great school system.
I feel the same way about college. I understand the arguments that college is not often worth the excessive cost if you look at it in terms of financial outcomes. But I didn't go to college for financial outcomes. I went because it was going to be (and was) a uniquely amazing adventure that I could never replicate at any other time in my life. I think going to grade school is the same thing.
Nothing can replace acting awkward around your crush in the hall, learning to navigate around the bully, bonding after class with a favorite teacher, enduring the horrors of PE or the excitement of a bomb threat, to name a few nostalgic examples.