If you think boarding a plane in the US is disorganized, try boarding a plane in pretty much any non-Western country. Boarding groups don't exist, lines have no width limitations, and it's a mad rush to squeeze on board. In many places, carry-on baggage restrictions aren't even remotely enforced or checked.

The most organized boarding experiences I've had in the West have been in the UK, interestingly enough. It seems the British are innately aware of how to queue correctly and in an orderly fashion. Japan and Singapore were also incredibly orderly.

I've been to a lot of places around the world, and I'd say the US is on the upper side of the middle of the pack in boarding efficiency and order, and it's better than boarding the plane in some European countries even. Considering the US market alone accounts for a significant chunk of all air travel globally, efficient boarding isn't exactly something people ignored. There's actually a lot of research that's gone into it.

I'd say the US is capable of doing things organized with large groups of people, but only if there is a social standard set for that situation and environment. Right now we have no such standard for an evacuation situation.