Sure I agree with that. I was only sharing my personal experience where, in my tank, it started with one Cory flashing, then it spread to the other Corys. From the Corys it spread to my other fish until all the fish were flashing. Very heartbreaking to see, then fish started dying. The Seachem Cupramine quickly cured the fish and stopped the flashing when nothing else worked. Cupramine is a chelated copper, so it is safer than Copper Sulfate on the plants and fish, but it still is potent.
It is important that we share these types of experiences so hobbyists can save their fish from same diseases. This is why I do this.
But, yeah I wholeheartedly agree; everyone must be sure of the disease and not treat recklessly.