Stallman's ethical argument is based on the principle that it is unethical to not help your neighbor if it is in your power to do so. His argument is that it is wrong for your child to enter into an agreement with the software company to not give his friend a copy, because the fundamental value of personal, human cooperation is made secondary to a corporate economic model. You don't have to agree with it, but that is the argument. If you want to make a food analogy, it is like shopping at a grocery store that forbids you to give the food you purchased to anyone else, no matter how hungry they are. Or buying sunflower seeds that you are forbidden to plant by their license.