It depends on how you step on it. If you slide your foot across, you might get a cut. And I receive glass splinters almost all the time. Not enough to convince me out of barefooting, but we shouldn't kid ourselves here.
Glass and stuff is mostly a problem for people who regularly wear shoes. Takes a little time for that unconsciousness or automatic ground scanning function to kick in. If you wore gloves all day for years then suddenly took them off I would imagine you would be getting burned by hot things wile cooking stubbing fingers skinning knuckles all the time.
That's a great analogy. Construction workers always have very tough hands. When you start going barefoot, it will inevitably take a while for your feet to become not only calloused and tougher, but also more resistant to pain. When you start cooking the heat always scares you a bit, but after a while you get used to it. The same goes for those uncomfortable surfaces that your soles aren't able to cushion out no matter how tough they are.
I find that walking on anything, including glass, pebbles or anything judged by most people to be a no no, is just a matter of going for it and not tensing up and being all tentative like most people tend to be.
There can always be exceptions but people don't have to start walking on rail road ballast out of nowhere. A trip to the mall or a walk around the neighborhood is something that doesn't really warrant shoes, except for the odd fear of dirt.
