That the system is in the black doesn't necessitate that program is not in fact a subsidy. If the market interest rate is 5% and the gov loans at 2%, assuming no defaults, the program will appear to be in the black while still subsidising borrowers at the expense of taxpayers. Moreover, when you say "fair for people like us to subsidize the people who pursue public service" you seem to imply that the tax is progressive when in fact is not since most people going to college are middle and upper middle class. Finally, this doesn't address the question of who is providing a public service. Are private for profit orgs not providing a public service?