I'm not sure I get the connection between a Coach's salary and student debt. There are a lot of schools that have low salaries for the football or basketball coach but their tuition is extremely high. Take for example Harvard or Yale or any Ivy League school has high tuition but low athletic salaries comparable. I can' t speak for every school but Louisville more than gets their money back on CBP's salary.
It's certainly not a direct connection, and I concede your point regarding CBP. But my point remains - that type of cash outlay is a very bad look for a public institution, funded by tax dollars and student tuition (which is largely funded by student debt). I don't know where the line is and I'm not about to suggest one, but I'm thinking it's probably south of Harbaugh's $9MM/year.
Like I said, I'm all "go free markets" whatever. If the NFL wants to pay Belichick $100MM/year or whatever, and their franchise and fans are willing to go for, well go for it. But public institutions, I don't know man, $9MM, $6MM, that's a lot of public money.