Why has William Ashby changed his political views in The Witch of Blackbird Pond?

One of the key themes of this exciting novel is the rising sense of opposition to the crown and how this is enacted through the opposition of the townspeople to the new decree of Governor Andros concerning land rights. It is in Chapter 15 that we see a reversal in the way of thinking of William Ashby. Formerly he was an ardent supporter of the crown, and yet suddenly he comes in to the Wood household to join the meeting of the men discussing their options:

Some time ago William had arrived, offered his usual courteous greetings to the women, and then, instead of taking his place by the fireside, had astounded her by knocking boldly on the company room door. More surprising still, he had been admitted, and there he had stayed, behind that closed door, for the past half hour.

When Kit asks Judith about what has brought about this sudden change of thinking in William, she tells her that William had begun to agree with Matthew Wood and his political ideas about two months prior to this when he had to start paying such high taxes on his land.