According to Rosenberg, the virtue that the Harry Potter series rewards is not moral virtue but learning, which she demonstrates is not the same as knowledge. Harry and his cohorts are united by their ability to learn and adapt, which I believe I mis-perceived as loyalty; in fact, they are united by a process and love of curiosity which is why they are able to reunite even after their numerous fights that break the bonds of loyalty.
I'm almost tempted to re-read the entire series from this perspective.