Choices
Hermione had made her choice the day she erased her parents' memory. And she made it again when Ron left Harry at the forest. She always knew what needed to be done. And her conscience was clear.
Perhaps that's the root of all problems. Maybe it all came down to it. Choices. Or the lack thereof.
Perhaps it all boiled down to the choices one made.
If only his father had chosen better and not sided with someone like the Dark Lord. If only he had changed sides and gone to Dumbledore for help. Then, perhaps, Dumbledore would have lived. Together with Harry, he would vanquished the Dark Lord much sooner.
And Crabbe would still be alive.