Is it just luck that we haven't had a sniper at a major sporting event?
We've had shootings in most other venues where large groups of people congregate. On top of lots of people in one place, few of these venues offer the exposure and the link to "what is Americana."
I know bags are searched etc. I'm certain, that sporting stadiums are examined from the point of view of where could or would a shooter hide. Sadly, I'd be willing to bet one day it will happen.
We are no longer naive, our societal innocence is no more.