The central argument of the American colonists against the Stamp Act that is not understood by the writer is:
that it is not the amount of tax that is the problem but rather the fact that the colonists were not involved in passing the tax.
This highlights the principle of "no taxation without representation," which was a core grievance of the colonists, emphasizing that they felt it was unjust to be taxed by a government in which they had no elected representatives.