And when they buy things, are those things denominated in fiat currency or in bitcoin?
By your logic if I exchange dollars for euros to spend on a vacation somewhere that means the dollar has failed ?
Now imagine you get paid in bitcoin, save every month for a holiday or a high value purchase. When the time comes to make the purchase you find out that your savings are worth less than 10%. How does it feel using bitcoin?
I tried to use bitcoin(as a merchant) but due its volatility it makes no sense to use it(as merchant or buyer).