People have weird ideas about seasoning. It is literally oil polymerized and bonded to the metal with high heat; but people act like it just rubs off. You can scrape seasoning off, but it’s hard. I need steel wool to do it.
I think these people complaining aren’t really seasoning their pans - just using dirty pans (i.e. the oil hasn’t fully polymerized).
It’s fine and good to wash cast iron - particularly if you had something corrosive in there. Don’t do it in the dishwasher (change in heat can be bad for it - same reason not to machine wash kitchen knives).
People who say washing your pan will remove the seasoning have not properly seasoned their pans or see food residue washing out and think it is the polymerized oils bonded to the metal that are washing out. If that’s the case, they are washing way too aggressively.