The opinion quoted by the OP comes from someone that wants to inspire FUD on this market by talking about what it is theoretically possible, but if we were to talk about that with any seriousness then we should be scared about everything as in theory anything can happen, however if we are being realistic about this, it is very unlikely for bitcoin to ever go down all the way to zero, as I would expect that an asset that can help you to retain some of your privacy and move your wealth without any third party interfering will always have some value.