For thirty years Jesus lived unnoticed among his community. In today's gospel, Jesus returns as a man of wisdom and knowledge.
Can you blame them for asking where he got "all this wisdom and these miraculous powers."? The people did what we all do, they cast up about who he was, naming his parents and relatives.
That's what is wrong with human nature. We are so petty and spiteful. Doing what was good and speaking wisdom made Jesus a threat to his townsfolk. They wanted nothing to do with him.
The truth, particularly when it comes from someone close to us, can be rather disconcerting. It is easier to ridicule the messenger than to listen to the message.