Population Pressure?
Let us admit that the thickness of the crowd MIGHT affect what's sensible? I've been in state fairs, and a thoughtless person with a package of firecrackers isn't unthinkable.
Were I carrying in a large crowd, and suddenly heard loud noises and screams, my actions thereafter wouldn't necessarily be entirely safe (for members of that crowd)..
mistakes do get made, and i'm not immune from them.
And I'm careful, mature, have a bit of training, and don't drink ..
Some more impulsive sort, with perhaps a beer or two aboard and scant life experience would arguably be even less safe.
While I can see the idea as an insult to off duty officers, BY GOD I'd rather be insulted than interred.
Considering the circumstances, ANY carrying might NOT be the safer alternative, from the event promoters perspective.
Now, in all fairness, were I involved in said decision, I'd try to explain myself very clearly, and quite possibly offer discount tickets, and not weasel about it.. how the policy was formed isn't clear, nor who formed it, and it would cost little to try to mitigate perceived insult.
If the fair has gone so far as to install metal detectors, then at least Someone thinks there's a real danger .. While that might be a strong arguement for extra security, and MORE official presence, I can certainly understand the idea that anyone (not in uniform) seen with a firearm would be presumed dangerous.
Reflexive assertion of ''rights'' should be tempered with deliberate effort to see not only 'the other side' but 'the big picture'. Sez me..