By 1776, declaring independence was the correct thing to do. There are two major reasons for this.
First, the British government was not giving the colonies enough in the way of personal rights or the right to self-government. The fact that the British would do things like setting up vice-admiralty courts without the right of trial by jury or that they would take away the right to self government in Massachusetts shows that they did not respect rights to the extent that they should have.
Second, the colonies were "big" enough in terms of population and economic output to be independent. They no longer needed Great Britain to support them. Because they did not need support and because Britain was denying them rights that they deserved, declaring independence was the right thing to do.