Chris, your response to the border patrol is right on. I experienced a similar reaction when I visited Israel about 9 years ago. People carried AK-47s over their shoulders everywhere, even in the mall. I will never forget how I felt when someone two people behind me in line at the food court had an AK-47.
Interestingly, I just found this quote in a research article published in 2011.
"School violence was significantly lower in schools where the security officers (guards or SROs) were in uniform (b = −0.292, SE = 0.112, p < .01) whereas school violence was significantly higher in schools where the security officers carried firearms (b = 0.456, SE = 0.108, p < .001)."
From "Evaluating the Relationship Between Law Enforcement and School Security Measures and Violent Crime in Schools." Journal of Police Crisis Negotiations, 11:2, 109-124 (2011).