I've been reading like a student (200+ pages/day, not counting work) recently, in preparation for exams, and, like a student, I'm brimming with idealism. It may not simply be youth that leads students to idealistic thoughts, but rather the confrontation with radical historical change over time. You can observe how much society changed--let's say in the Levant from the Chalcolithic (late fifth-most of the fourth Millennium B.C.*) to the Early Bronze Age (let's say 3300-2300 B.C.), with the development of early city-states, and then the thoroughgoing collapse of that social structure and a widespread return to seminomadic pastoralism for a few hundred years, followed by a rejuvenated "urbanism" (politism?) in the Middle Bronze Age. Even changing burial practices (to give a classic archaeological example) are evocative: The Early Bronze periods are marked by multiple graves, where a family would inter its members together--indicating at the very least a strong social connection and attachment to a place over generations, and I suspect rather more: a desire to remain with one's loved one in the afterlife. At the beginning of the Middle Bronze, the dead are buried alone--sometimes in graveyards, yes, but no longer sharing quarters with a spouse or parents or children (or all, and more) for all eternity.
So what does this all have to do with scholastic idealism? In short, seeing such radical change makes one realize that radical change is possible. Seeing radical change fall short, and sputter, collapse, and reverse itself--as at the EB/MB transition--but then burst forth again--in the great Canaanite city-states a few hundred years later--makes one realize that the path to change is never a smooth arc (either upward or downward!). Yes, it can be another way that smart people can be so stupid. But it's also another way that they can be so hopeful.
*Current academic habit is to indicate dates in "B.C.E." and "C.E." standing, it is said, for "Before the Common Era" and "Common Era." The old habit of "Before Christ" and "Anno Domini" ('in the year of the Lord') is felt to be exclusive (not to mention, well, wrong by about four years). Slapping a new name on something and calling it the "common era," in my opinion, both denies its origins, and implies that it's a commonly agreed upon era, when it's really one that was imposed by the military might of the Holy Roman Empire, and, more importantly, the administrative and educational capacity of the Catholic Church. The Republic of China, from 1912 to 1949 used the term "Western Era" for the Gregorian Calendar (thanks, Wikipedia!) a happy usage indicating both origins, foreignness, and (perhaps grudging?) acceptance on the basis of utility.
Physicists and geologists can use the more felicitous abbreviations MYA and BYA (millions and billions of years ago, respectively)--does that indicate a lower (more realistic?) opinion of how long their work will remain in circulation? C'mon, people, Thucydides thought he was creating "a possession for all time" and you can't write a Science article that will last five hundred thousand years? Well, maybe MYA and BYA are just CYA.
One last digression. Obviously, "anno domini" is a theological statement, and "before Christ" can be taken as a historical one. Thankfully, I'm in the happy position where I can focus my research on the 'negatively-numbered' years. Perhaps it would be an amusing challenge to write a dissertation on Hellenistic Judaism without using any AD/CE numbers. One could "go native" and use Seleucid dating, or the Livian standby, AUC, or perhaps merely reckon from the Creation of the World.