We have a welfare system that can step in when the parents can't take responsibility and this system only works when those parents are a small minority.
I think it's valid considering it's usually parents who pay for their children's schooling if it wasn't free. The benefit here is monetary, not academic.
That's an interesting point. On the other hand, where education is free it is so, to a large extent, because it is considered a worthwhile investment into a society's future.
I think it's a mistake to assign the educational benefits people receive (whatever age they are at the time) to their parents.