I think a lot of people tend to be under the assumption that the military has enough training to carry loaded weaponry around safely all the time. This is not the case. Go to any place there are guns (shooting range, firing line, gun show, gun shop) and you will see that safety is the number one priority. Not necessarily safety from other people and/or shootings like this, but safety from accidental discharge. When you are away from the firing line, mags are out, chambers are cleared and safeties are on. It’s no different here, really. I don’t believe that it’s 100% of a PC decision... even though that may be a part of it. It’s more for a stop-gap against accidents than anything else.
We may not see mags loaded in the guns, but that doesn’t mean they are defenseless. These guys are trained to load a gun and shoot in a matter of seconds.
An attack on the checkpoint would be over in a matter of seconds. I don't think you understand how long a second is under such circumstances.
...you will see that safety is the number one priority.
That's like not wearing a seat belt until you're sure the car is about to crash.
Not at the best schools. Having learned assorted lessons, many/most serious ranges have gone "hot". Training people to go "cold" gets people killed. Yes, there is risk at "hot" ranges - but military training MUST accept those risks, lest they lose more in the field. The situation in question isn't about training, it's about actual protection of a high-risk high-value target. You fight as you train - you practice "cold", you'll fight "cold". We've seen this many times, and many died thanks to such bureaucratic sentiments.
Rule #1 is "all guns are always loaded" - not just so you'll treat it like it's dangerous, but so it will be when you need it to be.