I worked my way through college doing security work, and can personally vouch that it's essentially the most worthless occupation on the entire planet. Well... maybe ant wrangling is almost as worthless, but it's damn close.
If you're an unarmed guard, the only real action you can legally take in the presence of violence is to place the suspect under citizen's arrest. Believe me, you really don't want to do that, as it's a one-way ticket to the unemployment line (and bad references from your employer to boot!).
Now armed guards, on the other hand, are scary people. They have roughly half the classroom training and gun-range time of police officers, and most states don't even require a psych evaluation. If armed guards had been the focal point of this incident, it's highly probable that the story would have unfolded a bit differently to everyone's detriment. :lol