Seriously, you need to do a little better in explaining what exactly do you mean. Rational person would buy bitcoin either: as a speculative investment, as a hedge to current monetary system, or for its utility (ie. to easily transfer money).
Guess what? A huge percentage of your beloved fiat money in banks are actually digital. Not everything is in paper money. And also, guess what? Some countries are already cashless, meaning that all(95%+) of their day to day transactions are actually digital. Does the intangible characteristic of their funds make it worthless? I don't think so.
And also, guess what!? Your beloved fiat money isn't backed by anything.