The American Revolution against British colonial rule was a 'populist mass movement' that the vast majority of American citizens would agree was a good thing.

This article reads a bit it was written by a British servant of the Crown giving advice to imperial administers on how to keep their colonists under control and head off any movement towards independence.

More generally, mass movements often arise in situations where a small group with elite privileges (e.g. the French aristocratic class before 1790) rules over a much larger relatively impoverished group lacking any such privileges. A similar situation arose in the American South at the height of the plantation slavery system in the first half of the 19th century (of 10 million people in the US Confederacy, around 3.5 million were enslaved, and the majority of the wealth was held by a small group of plantation owner elites).

Clearly, the author believes that mass movements are undesirable (since the author only references Mao and Hitler as examples of outcomes), but the French and American Revolution ushered in democracy on a large scale, which are generally good things. I suppose people who've been indoctrinated into belief in the superiority of the Ivy League elite schools system might think that democracy itself is unwise, and that rule by a small educated elite is preferable. Sometimes they'll even admit this in private, though rarely in public.