Several issues with the video above. First, the case study in the beginning took place in Illinois (where guns were illegal to carry up to very recently). That didn't stop the gunman killing 5 people.
Second, the video states "this training is already more than many states require in order to carry a firearm." While statistically true, the fact is that almost everyone who carries a firearm takes additional training, including practicing with it on a regular occasion. I train with a firearm once every two weeks for 4 hours - tactical drills, reloading, controlling breathing, CQC, etc.
Then they put a kid with a firearm and a long shirt in an experiment and automatically assume everyone will have the failings of the kid (who only practiced during the training provided in this demonstration). Laf. The instructor coming in also knew to shoot "Joey" because he was armed. That wouldn't happen in real life.
Next, when Danielle goes, she shoots the intruder (despite poor posture and standing up). If this were a real situation, the shooter would be DOWN. Without that weapon, the shooter could reload and continue his rampage. Again, they knew to attack her. Same with the third guy - they went for the guy with the gun. In a classroom setting, they're not going to know who has the gun.
At the end of the day, you can spew all the propaganda you want, but having a weapon is better for defense than no weapon at all.
And let's remember, YOU have no idea how to get all the illegal weapons off the street - which is the only way you're going to stop the shootings.