Ich is one of the most studied fish diseases out there. It effects the fish farming industry way more than people with fish tanks.
The facts are all out there. You just need to read them and understand them
FTW : the only way to keep ich out of your system for good would require having a DT, a QT and a tank to keep everything but fish to let any free swimming or hitch hiker ich die before getting in your DT. Oh and don't forget a hospital tank. Most people won't do this, so most everyone gets ich in the tank at some point.