What events push John Adams to be strongly in favor of Independence?

As a boy John saw his father Deacon Adams invite widows and orphans over for dinner. John as a boy was encouraged to visit a sick elderly neighbor, even though it was the sabbath. As a young lawyer John was expected to take his turn as a town trustee and supervise the rebuilding of a bridge. This was self reliance, taking care of your neighbors and community. As a young lawyer John saw the state assembly as the embodiment of this principal. The British attempt to close the legitimate state assembly went against everything John had been taught in law school. No King or parliament had the right to suppress local representation.

John believed in the law so strongly, he defended the soldiers at the Boston massacre, and got them acquitted.

When the British marched on Concord, there was no other logical choice. Fight to keep your rights, or submit to servitude.