That is hogwash. The only ones carrying weapons on a base are the MP’s and Federal officers (if present). Some soldiers may be carrying weapons heading to and from training, but I highly doubt they would be authorized to go after the bad guy unless they were directly under attack.
I know we occasionally drew arms (M16’s, M1911) when performing security details, like payroll guard. When I was in the Army in Germany, I had a loaded M1911 in my center desk drawer, who it was checked out to I never learned. I worked in a room with safes containing Pershing Missile fire tapes and firing codes and I guess I was expected to shoot anyone trying to mess with them. I never received any explicit training or instructions on the use of the weapon or deadly force or anything like that. I suppose they expected me to rely on common sense.
In a fire drill, I reported to the arms room and drew an M-16, the firing batteries sent details to evacuate the safes. We went into the building - armed - during a fire drill.
I agree, having a loaded weapon in CONUS is very unusual.