Not sure about the soap thing. It definitely strips more of the "seasoning" than just water in my experience. And it's my understanding modern dish soap contains some synthetics, and cast iron is very porous (I use the cheap kind, I think the kind for camping, lol), so I avoid soap. I just use very warm water and sometimes mechanical means (stainless steel scrubbers) to clean my cast iron. Tbf, just cooking very fat/oil heavy stuff restores much of the seasoning whenever it's lost.