It isn't a policy argument, it is a fairness in economics argument. Very strong stuff:
Pay them because the worst American tradition is taking things that aren't yours and calling it destiny or virtue or principle. Pay them because there is no nobility in keeping someone a dollar poorer than they have to be in exchange for honest work. Pay them because any system that deliberately makes people poorer is one of designed cruelty, even at this relatively small scale.
This has long been the hardest part of the ideal of amateur collegiate athletics for me to digest.