Think about it.
Think about all of the unintentional discharges you're heard of.
Think how show organizers have to be totally paranoid because of insurance and various agencies that want to put them out of business.
I'm a Life Member of Washington Arms Collectors. They are EXTRA strict, because they know they are the biggest "target" in the state. They operate on the presumption there are agents provocateur in every show (even if they don't catch them every time). Cameras are banned at WAC shows. Only members can buy and sell guns; anything else can be bought/sold by non-members.
It's just too easy to get into conversation, compare guns, put one's carry gun back, talk some more, pull the carry gun for one more control comparison or something, and make a slip.
Do I know people who will carry even knowing they'll be banned for life if caught? Yes. But those guns are in DEEP concealement.
By the rules: If I carry, and many do, I unload and tie wrap the piece, then put it back into my holster/belt.
In a WAC show, NO loaded magazines, NO magazines in guns (they even pull tubular mags from .22 rifles, and NEVER ammo on the same table as any gun that it will fit. They even put tie wraps on muzzle loaders.
Are there sicko types in the gun-hating crowd, who would surreptitiously load a displayed gun, in hopes of causing an accidental shooting? YES! They hate all gun owners, and an accidentally dead gun owner at a show would be exactly what they could use. These dirtbags do exist, and they don't all work for F-troop.
Even at the smaller shows, similar precautions are taken. I can't recall the last time I attended a show where tie wraps were not used.
No, in 2010 it's VERY unlikely you'll see any gun shows in America that let you carry loaded guns. The one exception to this is, of course, the Police. My buddy with a badge never had any problem carrying his loaded gun in a show.