I really really hate that sentiment. It's not even so much the "Life is tough" bit because, indeed, life does throw challenges at people and those challenges are sometimes difficult. It's the "Children need to learn" sentiment which has my hackles rising.
Because behind "they have to learn" is an implied "and it's going to hurt them" and somehow the speaker is just RELISHING the fact that they are going to suffer, and that suffering is Good For Them. Whenever I have encountered it, there is an edge to the tone of voice, an entire world view which believes that That Which Does Not Destroy Us Makes Us Stronger, and You Have To Suffer To Be Beautiful. The person saying it subscribes that well known magazine The School of Hard Knocks Weekly.
But I believe that they are wrong. People learn least well through suffering because the brain does not function as well under stress. The things people learn in stressful situations are not necessarily at all what those trying to teach them (parents, teachers, peers, whoever) are trying to teach.
Not all people who send their children to school are "Life is Tough and you have to learn to deal" people, and not all HEers are the opposite. Although the quote was brought to my attention by a HEer being criticised for her family's choice because "Life is Tough blah blah", I don't actually think the quote got anything particularly to do with school vs. HE at all.
The kind of person who says "You have to send your child to school because life is tough blah blah" is just as likely IMO to say "you have to leave your child to scream themself to sleep because life is tough blah blah" or "the rot set in when they stopped national service because life is tough blah blah" or whatever they happen to think you are being too "soft" with your child about. In the context of this original quote it happened to be school/HE. If the child in question was going to school, the criticism would be of helping the child make their sandwiches which was not teaching them that "Life is tough", or allowing them to wear a coat on a chilly day even if the clocks have already changed. The problem is with the Life is Tougher, not with whether anyone's children go to school or not.
By the way, I think that if school is horribly stressful for a child, they'll be better off out of it educationally and socially, long and short term, rather than self-harming or committing suicide or anorexic or waiting to see if the last lot of bruises heals before the next lot arrives or weeping every Sunday night as the new week begins.