You gave an extremely detailed response which was a pleasant surprise. I do not suggest that students should pay for thier education as a 'punishment' but rather as a way to allow them to value it. Most students in my school believe that they are required to attend school for some vague 'benefit to society', and they have been lead to believe this because they are literally being begged to accept the most valuable treasure the world has to offer. Is it any wonder that they suspect its value? My solution is stop begging and start demanding that students: follow directions, attend classes and complete assignments.
You are right that the goal of education must be clearly defined, I suggest that in very general terms the purpose of education is to promote positive growth in our students. (intellectual, physical and emotional)
You are also correct in suggesting that adversity without direction or purpose does not promote growth. So many educators today have sold students, society and even each other on the theory that 'learning is fun' that our students have been conditioned to reject anything they perceive as challenging, difficult or painful and in doing so are well on the way to an 'idiocracy'. For a more detailed description read Mortimer Adler's, "Invitation To The Pain of Learning." In my book, I spend an entire chapter outlining ways that instruction can be made more rigorous.
The way to hold students accountable is by allowing students the opportunity to fail. A baby learns to walk by falling (and getting up) over and over again, imagine if a misguided parent decided to save thier baby from the traumatizing effects of failing (failing) and followed them around with arms outstretched. Many of today's educational leaders believe that they are 'helping' students with the 'failure is not an option' philosophy. Unfortunately they don't seem to realize that if failure is not POSSIBLE then there can be no success.