That's true of all currencies. It's just a shared delusion that the coin or paper has any value. That in itself has value, as otherwise you left with bartering with specific goods that have value to the person you're trading with - a significantly less liquid market than the one featuring the shared delusion.

In that sense, there's nothing special about bitcoin. It's just another shared delusion, just with fewer believers. As long as there are believers, there is value. The stronger the belief, the greater the value.