Honestly, the “no soap” thing is an exaggeration. I pretty much only cook on cast iron, and I regularly will use a little bit of soap if the pan is particularly greasy (e.g. after deep frying). It’s never affected the beautiful black patina on my pans. I sometimes see other people’s cast iron that still has a sticky oily sheen on it, and know that they’re too worried about the “no soap” myth.
Much more important is drying it well. Leaving it damp even just overnight will cause it to develop a little bit of rust. But even that’s not actually too much of a problem. It’s impossible to permanently damage a cast iron pan, unless you subject a very cheap one to sudden temperature changes and it shatters.
As for “disinfecting,” I recently got a new pan (I needed a larger dutch oven) and noticed the little tag says “if you’re worried about germs, don’t be! An empty cast iron pan on the stove heats up to 400ºF in one minute.”
