Quite ironic, people against gun control almost universally make the comment that, "If a criminal is determined enough, they'll commit the crime anyway [with or without a gun]". So, applying that logic to this situation, if a group ever planned an attack on an airport, the attack wouldn't exactly be dependent on the airport having armed security or not.
In any case, Just about every major airport has at least some armed security/police officers on duty. Over here for example, every international airport has a small detachment of AFP (Australian Federal Police) officers stationed there.
Still, using a hypothetical situation from a game isn't a good way to prove your point. Frequently, those kind of games, appealing to a mainstream audience, flaunt realism and substance for entertainment.
What kind of point are you trying to prove then? - "Teachers are humans, Police Officers are humans, they're both fallible. Therefore, they should both have guns!"
I tend to look at the occupational environment. Police officers, in their line of work, are almost entirely in a sphere of dealing with criminality, unruly behavior and dangerous individuals. Therefore, to protect themselves and others, and to do their jobs effectively, they need the necessary tools of coercion, such as firearms or tasers.
Teachers on the other hand, work in a completely different occupational environment, one that does not facilitate, in my view, the carrying of firearms.