This is another common misconception, and one I’ve tried to wrap my head around for a while now. I suppose when someone says this, they’re thinking of what could happen if they simply pulled the shoes and immediately took their horse over rough trails or rode on cement all day long. I assure you, most horses would be very sore.
Would it wear the hoof wall down some? Probably so. But who in their right mind would ride a horse barefoot over rough terrain when his feet obviously aren’t ready for it?
Transitioning to barefoot often takes time. Horses shouldn’t be expected to make the switch overnight. But with the proper trim, diet, and movement (am I sounding like a broken record yet?), the sole of the hoof will toughen (callous). This process will take place more quickly in an arid environment.