Final answer:
The colonists' main concerns were unfair taxation and lack of representation in government because they believed in the right to have direct representation in Parliament to consent to taxes, a right grounded in the English Bill of Rights of 1689.
Step-by-step explanation:
The most concerning complaints to the colonists were unfair taxation and lack of representation in government. These two issues are interrelated and reflect the core principle of no taxation without representation, a stance based on the belief that only elected representatives should have the power to levy taxes.
The colonists saw unfair taxation as a denial of their rights as Englishmen under the English Bill of Rights of 1689, which they argued should allow them to have direct representation in Parliament to consent to any taxes imposed on them. On the other side, the British Parliament had difficulty understanding this concept, as they believed in the idea of 'virtual' representation, where representatives elected by a portion of the population represent all subjects, including those unable to vote.