The math (generally speaking) says pay low-interest debt as slowly as you can and invest the difference to come out ahead. If you have the discipline, hard to argue with the math. In this case, we're talking good (pay-off the debt) vs. better (get better long-term results by investing), so paying the loans down first isn't "bad" per-se, just sub-optimal.
The problem a lot of people run into is that they pay low-interest debt as slowly as they can and spend the difference. This is good vs. bad.
Then of course there is potentially a psychological benefit to being debt-free, but that is hard to quantify.