The root of the issue is that the person asking the question is starting with an assumption (I need shoes) and asking about the base (the feet), instead of starting off at the base, and asking a question about making an assumption.
Let's start with the facts:
- We were born barefoot -- completely naked.
- Running shoes are a fairly recent invention.
- We evolved to be runners.
Given that we start off life without shoes, and we evolved to be runners, it would follow simply that we are born to run without shoes. If we leave out culture, peer/parental pressure/indoctrination, and look purely at physical reasons we would wear a foot covering, what would that list look like?
- To provide warmth and/or prevent heat loss.
- To protect the skin against extreme hot or cold.
- To protect the skin against protrusions such as jagged rocks, thorns, cacti, etc.
With that said, the simple answers to the question "why wouldn't you run barefoot?" are:
- Too hot, the skin on my feet will burn.
- Too cold, my feet will get frostbite.
- I'm running over a field of broken glass and syringes, blindfolded. Or less sarcastically stated: I've kept my feet in shoes my entire life and I'm afraid to let them out, because they are incredibly sensitive.
If you're currently running in shoes, ask not why I choose to go barefoot, but why you choose to go shod. Is it because that's how people always have done it? That's simply not true. Is it because you're afraid of the scorn and odd looks from others? Is it because you're afraid your feet will respond as if you're the princess and the pea?