There are two main reasons that Diabetics are advised not to soak our feet:
- Soaking feet for more than 3-4 minutes causes the skin to soften and break up easily, which doesn't heal well.
- Impaired circulation will cause the skin to burn very easily; water temps in excess of 92F/33C can easily burn the skin.
As for pumice stones and callous scrapers, the controversy is that a callous or corn is the body's natural protection against irritation and thus shouldn't be removed; some physicians suggest a better solution is having orthotic inserts made, special shoes, or having shoes stretched to reduce irritation. The majority of podiatrists (that I'm aware of) do file down callouses, though.
Personally, I do use a footbath occasionally, but never for more than 10 minutes and only with lukewarm water. I'd imagine that the words of warning are meant more for diabetics with tenuous control, and as always YMMV