"In World War II, only 15 to 20 percent of combat infantry were willing to fire their rifles. In Korea, about 50 percent. In Vietnam, the figure rose to more than 90 percent."
 - https://www.amazon.com/Killing-Psychological-Cost-Learning-S...
Several years ago at our introductory fall faculty meeting (where we also introduce brand new faculty to everyone), our head of counseling services addressed the faculty body with the following remarks:
"I cant tell you the medications these students are on but it's scary."
"The next Virginia Tech shooter is on our campus right now."
Were I prone to believe his hysteria, I would carry on campus whether legal or not. However, he struck me as not terribly competent (and maybe sampling some of the students' meds himself) and my interactions with students, even the obviously not all healthy ones, does not make me overly concerned for my safety. It helps that I have nearly 20 years of a particular type of training that emphasizes awareness and peaceful resolution.
But that lads to me address a common refrain I see whenever this topic arises, that only faculty with military/police training should CC on campus. The presumption is that they are properly trained, but that training is disparate. Active duty police only hit what they fire at ~30% of the time (compared to 10% for gang members, I believe but I cannot find that study readily). Military infantry tend to be much higher (~70% iirc), but we tend to stereotype everyone in the army as infantry. One friend of mine spent 20 years in aviation repair work and even though he was deployed never came anywhere close to firing a weapon. He had the basic training and then that was it. However, I also grew up in a rural area where shooting was as common as grilling out or hiking. I knew several people who are experts in firearms who are not "government trained." Many of them I don't think are psychologically ready to handle having to potentially take a life, but several are. u/Geometer99 mentioned the PTSD that would come with having to shoot someone (much less a student you know) and that is very real. One of my combat veteran friends recommended a text written by a military officer and Psychology Ph.D. about that topic and how hard it is for >90% of people to actually shoot at another person. The book is called On Killing and was a very interesting read if a bit redundant between some chapters. It was very fascinating to learn about conditioning (and de-conditioning) techniques used by militaries and other groups.
When it comes to my colleagues, most of my colleagues could not fathom operating a firearm and many are afraid of weapons; there are a tiny handful I would trust. One has several years of military training from his home country. Another has the demeanor. Another trains in the same program I do. But we all have something else in common; I don't think we would carry on campus unless condition were so horrible as to make the likelihood of needing immediate lethal protection readily available. Fortunately, college campuses are very safe and violent incidents are very rare and the climate is not conducive to needing a firearm. My campus borders a really bad area of town and has had a few incidents (and I know several students have weapons on campus). It did only take them two years to park a police cruiser in the parking lot on the edge of campus where the drug deals commonly happened and armed robberies happened fairly often too. But even with that mixing of college and town elements, it has been fairly secure (just don't leave valuables in your car in the far lot). I and my colleagues don't need firearms. But niggling in the back of my contrarian mind is that absence of need should not equate to ban...
Haven't read this book since high school, but I think it might touch on some of what he's talking about:
There's a book I strongly suggest you read: On Killing
The fire rate (actually engaging the enemy) went from 10% in WW2 to over 90% in Vietnam.
I highly suggest reading On Killing: The Psychological Cost of Learning to Kill in War and Society by Dave Grossman. It gives excellent insight into how the military desensitizes people to killing and the effects it has had on soldiers, past and present.
This is the book i read on the subject.
This book talks about the natural aversion we have when killing another human and the study they did after WWII and how they learned to train today's soldiers to kill more effectively. The main method is the use of life-like targets from silhouettes to mannequins. Also the use of video like games for training, they learned this from the kids who played "Duck Hunt". The kids who grew up playing "Duck Hunt" significantly cut the learning curve how to shoot a pistol and hitting the target.
I've hear the same theory, never heard of whatever youtuber you're referring to.