They say it's illegal because of disease, apperantly our bare feet pick up and distribute a lot of bacteria and disease on floors, more so that shoes of course :)
Yeah, you can get athletes food and things like that if you happen to be exposed to it. But since most people in stores are wearing shoes anyway you won't be distributing anything that that's not already there.
I walk barefoot all over Boulder, on the sidewalk, on the street, on Pearl Street Mall. I go into all businesses possible without shoes and usually no one has noticed. It helps to wear a long skirt. I've neer to my knowledge gotten any disease that way. I actually got athletes foot from WEARING shoes!
When i've been dancing in places which also serve alcohol owners have been genuinely concerned that i would step on boken glass, this is reasonable. However if people go barefoot enough the skin with become very strong like leather. One day recently i was wondering what that crunchiness was under my feet and found it was a shattered light bulb!