I suspect that your TA is referring to the diminishing effect of two currents of American culture. The first is the portrayal of the Antebellum south in the media. The second is the "Lost Cause" tradition of slavery era revisionism.

I'll start with the Lost Cause because although I doubt that it had as much an effect on your classmates as Hollywood, it is more pertinent to both your question and the subreddit.

In the wake of the Civil War the South was obviously psychologically shaken. The first aim of the Lost Cause narrative was to assure southerners that there was nothing they could have done to win the war. They had been beaten by overwhelming numbers and industrial might.

This is the section where I was going to repeat the often stated theme of the south having an ingrained military tradition. A little more research proves that this is controversial, so I will just link to this book introduction.

In any case, the Lost Cause narrative developed from just reassuring southerners they were not to blame for defeat into a story that totally revised the history and causes of the war.

One of the biggest efforts of the revisionists was to both insist that the Civil War was fought over something, anything, other than slavery. This is how you get people calling it "The War of Northern Aggression" despite the south firing the first shots and preemptively seceding just because Lincoln was elected.

It is also how you get people like Judge Napolitano from Fox News going on the Daily Show to say that the civil war was about "tariffs."

The Lost Cause narrative changed the aims of the South in the Civil War from protecting the institution of slavery to the more noble sounding aim of protecting state's rights. It is this "State's rights" argument, a branch of which is obsessed with tariffs, that has not only dominated the talking points of defenders of the Confederacy, but that made it into many textbooks. This was a conscious decision by the leaders of Lost Cause movement. Here is an article with a lot of good history on this effort, despite its inflammatory title

Probably the biggest effect on the way young people view the Antebellum era comes from popular media. In recent years movies have been pretty staunchly anti-slavery. 12 years a slave won the Oscar for Best Picture while showing the brutality and inhumanity of slave holding. It's worth mentioning that this was based on a true story of a free black man in the north being kidnapped and held in slavery in the south.

12 years a slave came hot on the heels of Django Unchained which also showed the brutality of slave holding. Much to my own surprise, I also found out just now that it was Quintin Tarantino's highest grossing film.

Current movie treatment of slavery are a big departure from the way the subject was treated in the past. One of the earliest "blockbuster" movies (in quotes because this was before the blockbuster term was invented) was the movie The Birth of a Nation. This movie, the first movie to ever be shown at the White House, depicted the KKK in a heroic light. It dealt more with the Civil War and reconstruction than the antebellum period, but it does show how race was treated in the movies.

A better example of Antebellum treatment comes from "Gone with the wind." This film, which may be the popular movie of all time, is probably the cultural force most responsible for the "Disney Princess" view of Antebellum plantation women who just happened to own slaves. The big white houses, beautiful long dresses, elaborate hairdos and luxurious grounds of the time and place are tailor made for a Disney princess view of the times.

Despite the more fun nature of the film discussion above, I will point out that both "The Birth of a Nation" and "Gone with the Wind" are considered to be part of the Lost Cause movement.