This is an interesting thread. I agree with those who say work is productive and builds character. However, as some have pointed out, work doesn’t have to be for pay.
Those of us like the OP have the luxury of choice…and realize it. My daughter probably spent much more than 10 hrs/week “working without pay” for her RSO. She spent many hours organizing philanthropic fundraisers and service projects. I believe one event raised over $10,000 for an excellent cause! 
So to the OP, I would say, talk with your son about how he can make his time meaningful on campus. It will make for a more enjoyable and yes, productive college experience.