I disagree, as you well know. Yes, you should never use the small/small combination but you shouldn't use the big/big either. But with the chain as slack as El Gato27's, you risk chain bounce that can trap the chain in a chain stay or the chain can end up wrapped around the derailer and will end up tearing the derailer off the mount. In my experience, this kind of damage is far more likely and far more common than damaged caused by having the chain too short.