"ANOTHER F***ING STEP WITH THAT PAPAYA AND I'LL BLOW YOUR F***ING HEAD OFF!"

A dramatic example, but I think it makes sense for the guards to be armed because even though they may have cleared security somewhere, security isn't the same everywhere. It may be a lot easier to sneak a kilo of cocaine from Nicaragua than it is from say... New York City. And if you are a professional drug mule, your living depends on getting whatever it is to the "consumer" and the money is good, it would take a lot to stop you from running out of the airport at full speed, i.e. a gun.

And yes, a lot of people are lazy, but it's pretty great when you've been hauling a heavy carry-on for 1/4 of a mile.