I don’t think the authors are as pretentious as the readers are lazy.
This is really taking a sharp detour into IMHO country, isn’t it? 
Well, It’s a second year undergrad course, and there is no history prerequisite. I’ve no idea what the audience for the actual text is, however; I’m sure it could just be a case of the course organiser liking something a little too complicated rather than deliberate obfuscation by the author; he could very well have been aiming at PHDs (though I doubt, then, that I’d have made as much sense of it as I did! :))
I have no idea what the last two are, but I’m fine on the others. I still fail to see what phrases like “antebellum” provide that a simpler english translation wouldn’t. I have serviceable Latin, and I can assure that there is no subtle difference between “antebellum” and “prewar”.
My French is weak at best, but does “reason for existing” lack something “raison d’etre” has? “A quality that I can’t describe’” is a perfectly serviceable definition of “je ne sais quoi”. Ditto Zeitgeist and I’m sure the final two have possible translations, too.
The point is that there is no reason for using these phrases. Never is there such a fine shade of meaning needing to be imparted as to require a non-English phrase. “Gemeinschaft” and “Gesellschaft” are easily definable, and basically were, in the examples I partially quoted. Had the author simply used the words “community” and “society” and a simple definition like the site posted did, there would have been no confusion.
Why? Because they aren’t constantly familiarising themselves with foreign words? The reason for learning French should be to communicate with a French speaker, or to read French texts, or simply for the hell of it. Not to read English. Fiction excepted, of course; common foreign phrases are certainly welcome if spoken by a character of that language: “‘Je m’appelle Pierre’, the man in the beret said”, for example.
I simply don’t see a legitimate reason for introducing words much of your audience may not understand for no real gain in non-fiction.
But there is a subtle difference in English usage here. Nobody could naturally refer to pre-1939 Germany as “antebellum Germany”, but “prewar Germany” sounds just fine. For whatever reason, “antebellum” has come to be specifically associated with the American Civil War. Even academics don’t use it in writing about other wars.
If anything, it’s often used less as an obscure piece of jargon and more as a lazy cliche when discussing the pre-Civil War South.