There's an argument against modern shoes, especially so called "sports" shoes. They have terrible ergonomics that crush your toes, deform your foot arch, and weaken your feet with their unnaturally raised toes and heels and exaggerated padding. Curiously enough, "running shoes" could be especially bad if you actually use them to run, because their allow you to do so in a way that impacts your knees and hips really badly, slamming heel first.

He may be referring to that.