Why did colonists oppose the Stamp Act?

Colonists opposed the Stamp Act because they believed Parliament had no constitutional authority to tax them since they had no elected representatives in the House of Commons, a principle they captured in the slogan no taxation without representation. The argument rested on a long tradition of English liberty stretching back to Magna Carta in 1215 and the Bill of Rights of 1689, both of which held that the Crown could not levy taxes without the consent of representatives. Colonial assemblies had been raising their own taxes for more than a century by 1765, and most colonists insisted that those assemblies played the role for them that Parliament played for Englishmen at home.

Patrick Henry's Virginia Resolves of May 1765 declared that only the General Assembly of Virginia had the right to tax Virginians and warned of the consequences of any other course. The Stamp Act Congress meeting in New York in October 1765 issued a Declaration of Rights and Grievances stating that the colonists could not be represented in Parliament because they could not vote for its members and that taxation by consent was an essential right. Daniel Dulany of Maryland published "Considerations on the Propriety of Imposing Taxes" in 1765 dismantling the British counterargument of virtual representation, the claim that Parliament represented all British subjects regardless of whether they could vote. Colonists pointed out that even great English manufacturing cities like Birmingham and Manchester sent no members to Parliament, but unlike colonists they shared geography, culture, and constant lobbying access with members from neighboring boroughs.

James Otis in Boston had argued in 1761, during the writs of assistance case, that an act of Parliament against natural equity was void, planting a seed for later constitutional review. The colonists also distinguished between external duties regulating trade, which they accepted as a feature of empire, and internal taxes raised purely for revenue, which they rejected as the exclusive province of their own assemblies. This distinction broke down later when the Townshend duties of 1767 attempted to tax imports for revenue, and colonists then refined their objection to oppose any parliamentary tax aimed at raising money.

The deeper grievance was political. If Parliament could tax property without consent, colonists reasoned, it could take any property and ultimately reduce them to dependence. The Stamp Act crisis therefore moved beyond a question of tax burden to a question of self government, framing the constitutional argument that would carry through the Revolutionary decade.