It's an arms race. Police in other countries generally don't need to be so heavily armed because the populace is generally less armed, hence only the most serious crimes involve guns.
Whenever I read "if guns are outlawed only criminals will have guns" I think of how successful other countries have been in driving up the bar to there being a gun involved in crime. In places where gun control is enforced a typical 7/11 robbery does not involve a gun, they are reserved for high end bank jobs and the like because they are simply too hard to obtain and the penalty for using them can be made correspondingly high.
If Barcelona is doing better, maybe someone from SFO shoudl go there and find out why.
1. There's lots of light in a cinema, a big bright image lights up the audiences faces. I would have thought ample light to run a regular inexpensive CCTV camera pointed away from the screen toward the audience. That not just locates offenders but provides evidence too. More light can be added in the form of IR as others have noted.
2. NV goggles are expensive and having the staff roam around in them adds even more cost.
3. Once the NV goggles have the sensitivity turned right down to allow for the brightness of the screen, I would have thought that would render them not much better than human eyesight.
I imagine this is a scare tactic and nothing more, maybe there'll be a couple of sets of rented goggles moved from theater to theater and "paraded around" to scare people off.