I think minors joining social media or forums should require parent permission. There’s too many weirdos out there, and too much self harm from sharing too much information.
This is already allowed for under-13s, but almost no site/service actually allows for that. I imagine this would have similar results with it being a functional ban and the kids just all signing up as '18 year olds'.
I think it would, and I don't think HNs algorithm for ranking is abusive or toxic at all.