In the days after 9/11, government sent military to the airports to reassure the safety of air travel. However, having loaded guns around that much people would be extremely problematic so they removed any ammunition from the guns. So there they were, standing around with guns that had no ammunition in them, and people felt safe.

The goal of airport security is to make you feel safe by knowing other people have to go through the same ordeal (ie, security theater). It is more akin to hazing rituals than actually security.