Note that neither Dr. Gutzman nor Dr. McClanahan endorse the Constitution in toto as the absolute best instrument possible. What they do in the lectures such as this one is, as scholars, point out the difference between what was ratified (and thus ought to have been enforced) vs what was actually done, and they note that “it sounds good in this case” or “it achieves some policy result someone [including perhaps we] prefers” is not the same as “it follows the constitution.
This was one of the good and clearly-made points in some of the lectures I critiqued earlier; that they might agree with the policy aims that some late 19th/very early 20th century Courts “read into” the Constitution in striking down economically ignorant state laws, but 1) the Court was not given the power to do so under the Constitution (though arguably some of these cases would have fitted under the Contracts Clause, when they struck down the laws on the basis of “substantive due process,” that was incorrect and improper) and 2) case-laws such as these build up a storehouse of trouble for later generations.
People who accumulate power and transgress limits on their power usually do so for reasons they think of as serving a good purpose. Even the “bad guys” in these political dramas who were also enriching themselves thought that the goals and political system they were trying to create would be for the greatest good; they justified their various schemes on, well, utilitarian grounds (though the ones in the Founding period came a generation or two before “utility” as such became commonplace terminology).