What did the Founders mean...

[friendly_iconoclast]

101. I see ipsedixitism is now sharing space with 'proof by assertion'

Conventional wisdom is usually correct, it is NOT 'usually wrong' or 'almost always wrong' as you put it.

https://en.wikipedia.org/wiki/Ipse_dixit

Ipse dixit -Latin for "he himself said it"- is an assertion without proof; or a dogmatic expression of opinion.

The fallacy of defending a proposition by baldly asserting that it is "just how it is" distorts the argument by opting out of it entirely: the claimant declares an issue to be intrinsic, and not changeable...

...In the late 18th century, Jeremy Bentham adapted the term ipse-dixit into the word ipse-dixitism

Bentham, Jeremy. (1834). Deontology; or, The science of morality, Vol. 1, p. 323; excerpt, "ipsedixitism ... comes down to us from an antique and high authority, —-it is the principle recognised (so Cicero informs us) by the disciples of Pythagoras. Ipse {he, the master, Pythagoras), ipse dixit, -—he has said it; the master has said that it is so; therefore, say the disciples of the illustrious sage, therefore so it is."

https://en.wikipedia.org/wiki/Proof_by_assertion

Proof by assertion, sometimes informally referred to as proof by repeated assertion, is an informal fallacy in which a proposition is repeatedly restated regardless of contradiction.[1] Sometimes, this may be repeated until challenges dry up, at which point it is asserted as fact due to its not being contradicted (argumentum ad nauseam).[2] In other cases, its repetition may be cited as evidence of its truth, in a variant of the appeal to authority or appeal to belief fallacies.[3]

This fallacy is sometimes used as a form of rhetoric by politicians, or during a debate as a filibuster. In its extreme form, it can also be a form of brainwashing.[1] Modern politics contains many examples of proofs by assertion. This practice can be observed in the use of political slogans, and the distribution of "talking points", which are collections of short phrases that are issued to members of modern political parties for recitation to achieve maximum message repetition. The technique is also sometimes used in advertising.