A common argument against a convention for proposing amendments is that the 1787 Constitutional Convention delegates were a bunch of lawbreakers who disregarded their trust. From this, the critics deduce that the commissioners at an Article V convention might do so as well.

Note that the critics do not claim any of the other 41+ conventions of states and colonies exceeded their powers. (Most seem to have no knowledge of those conventions.) Instead, they place all their marbles on their belief about a single conclave held over 200 years ago.

But their belief is simply wrong. The charge that the Constitution’s framers exceeded their power is an old slander invented during the ratification debates by opponents of the Constitution. Modern scholarship has repeatedly shown it to be false: See here and here. Yet critics continue to repeat it, just as if it had never been rebutted.

Part of the “evidence” against the Framers is that they never claimed they had authority to propose a new form of government. This assertion demonstrates ignorance of the historical record. In fact, Framers repeatedly explained why they had that authority:

• James Madison of Virginia, in Federalist No. 40, argued that the commissions issued by the states were the source of the delegates’ power—not a limiting resolution of the Confederation Congress. The commissions issued by all states except Massachusetts and New York granted authority to propose whatever was needed to render the political system “adequate for the exigencies of the union.”
• On June 16, 1787, according to Madison’s notes, James Wilson of Pennsylvania stated on the convention floor that “With regard to the power of the Convention, he conceived himself authorized to conclude nothing, but to be at liberty to propose any thing.”
• On Jan. 17, 1788, Charles Cotesworth Pinckney of South Carolina addressed the issue in his state’s legislature, saying:

“[I]t had been alledged, that when there they exceeded their powers, he thought not; they had a right, he apprehended, to propose any thing which they imagined would strengthen the union, and be for the advantage of our country; but they did not pretend to a right to determine finally upon any thing—the present constitution is but a proposition which the people may reject….”

• On July 24, 1788, William Davie of North Carolina addressed the “lack of authority” charge at the North Carolina ratification convention in this way:

“This objection has been industriously circulated, but I believe, on a candid examination, the prejudice on which this error is founded, will be done away. As I had the honour, Sir, to be a member of the Convention, it may be expected I would answer an objection personal in its nature, and which contains rather a reflection on our conduct, than an objection to the merits of the Constitution. After repeated and decisive proofs of the total inefficiency of our general government, the states deputed the Members of the Convention to revise and strengthen it: And permit me to call to your consideration, that whatever form of confederate government they might devise, or whatever powers they might propose to give this new government, no part of it was binding until the whole Constitution had received the solemn assent of the people. What was the object of our mission? ‘To decide upon the most effectual means of removing the defects of our federal union.’ This is a general, discretional authority to propose any alteration they thought proper or necessary.”

For additional information correcting the claim that the 1787 convention acted illegally, see here, here and here.